# PassthePSA: PSA revision notes (full text) Source: https://passthepsa.com/psa-revision/ # How to revise for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/how-to-revise/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: Revise for the PSA by practising questions with the BNF open, not by memorising doses. Attempt each item from memory first, then check it against the BNF, record every error in a log, and revisit the log weekly. Add timed sets at 36 seconds per mark so that BNF look-ups become fast and automatic. ## Why should PSA revision start with the BNF? The PSA is an open-book assessment: the online BNF and BNF for Children are available throughout, so the skill being measured is using them well to prescribe safely. Revision that treats the exam as a recall test spends effort on the wrong thing. Make the BNF your daily tool from the first session. Open it for every practice item, find the answer in it, and note which part of the monograph held the answer (indications and dose, renal impairment, interactions, contra-indications). Familiarity with the layout is worth more than any single fact. - Use the search box and the treatment summaries, not browsing from the front. - Learn where renal, hepatic and pregnancy advice sits in a monograph. - Practise reading the dose under the correct indication, not the first dose listed. ## What is the core revision method? Use a three-step loop: attempt, check, record. The loop works because trying to retrieve an answer before looking it up strengthens memory and shows you what you do not know. 1. Attempt the item from memory or reasoning, committing to an answer or a written prescription. 2. Open the BNF and check the drug, the dose for the indication, the route and any patient modifier. 3. Record anything you got wrong or had to look up for longer than expected. Do this in short daily blocks rather than occasional long sessions. Spacing the same topic across several days beats doing it once in bulk. Mix topics within a session so that you practise recognising what each question is asking. ## How do I keep and use an error log? An error log is a running list of every mistake, kept in one place, with the reason for each. Reviewing it is the highest-yield revision activity because it targets your own weaknesses. For each error write four things: the topic, what you did, what was correct, and the cause. Classify the cause, because the fix differs. Cause | Example | Fix --- | --- | --- Knowledge gap | Unsure of a monitoring requirement | Read the BNF section, then retest in a week Look-up failure | Took the wrong indication's dose | Practise finding that section Writing error | Dose written as a volume | Rehearse the prescription format Misread question | Ignored the renal function given | Underline the patient details first Time pressure | Guessed with minutes left | Run timed sets Review the log weekly and retest the items you got wrong. Retire an entry only after you have got it right on two separate days. ## What should I learn and what should I look up? Learn the things you need in order to know what to look up, and look up the details the BNF holds. Time in the exam is too short to learn what you could check in seconds, and too short to look up everything. Learn | Look up --- | --- Which drug class suits which problem | The exact dose for the indication The high-risk medicines and their main hazards | Renal and hepatic dose adjustments Which medicines interact in dangerous ways | The detail of a specific interaction How to write a safe prescription | Whether a route or formulation exists Basic calculation methods and unit conversions | Maximum doses and infusion details Test yourself on the left-hand column without the BNF. Practise the right-hand column with it open and a clock running. ## When should I start timed practice? Start timed practice once you can find answers in the BNF reliably, and use the exam pace of 36 seconds per mark. The paper has 60 items, 200 marks and 120 minutes, so a 2-mark item gets about 72 seconds and a 10-mark prescribing item about 6 minutes. - Begin with untimed accuracy work, then timed sets of 10 items, then a full paper. - Time each section style separately to find where you run slow. - In review, note the items where you spent too long, not only those you got wrong. - Decide in advance when to move on from a stuck item and return to it. ## How does revising for an open-book exam differ? An open-book exam rewards efficient look-up and sound judgement over recall, so practise the process, not only the facts. The risk is false confidence: having the BNF to hand does not help if you do not know what to search for. - Recognise the clinical problem quickly, because that tells you where to look. - Search for the condition or drug, then read the heading before the numbers. - Check the patient details every time: weight, renal function, allergy, other medicines. - Check which resources the exam provides on the official PSA information, and practise with those. Note: Doses: any numbers you meet while revising should be confirmed in the BNF. These notes teach method, not doses. ## Check yourself - What are the three steps of the attempt, check, record loop? - What four things should each error log entry contain? - Which parts of a BNF monograph hold renal, interaction and contra-indication advice? - How many seconds per mark does the exam allow? - Why is it a mistake to take the first dose listed in a monograph? - Which of your last five errors were look-up failures rather than knowledge gaps? ## Questions people ask Q: Should I memorise doses for the PSA? A: No, not in general. The BNF is available throughout, so concentrate on finding the right dose quickly and on the few stable facts you should know without it, such as the high-risk medicines and the safe way to write a prescription. Q: How do I get faster at using the BNF? A: Practise with it open on every item and note which section held the answer. Timed sets at 36 seconds per mark then build speed. Q: Is an error log worth the effort? A: Yes. It turns mistakes into a personal revision list, and retesting the items you got wrong is more efficient than rereading material you already know. Q: Should I revise in long sessions or short ones? A: Short, regular sessions spread over several days are more effective than occasional long ones, and mixing topics within a session helps you recognise question types. ## Related notes - PSA study plan for 2, 4 and 8 weeks: https://passthepsa.com/psa-revision/study-plan/ - Common PSA mistakes that cost marks: https://passthepsa.com/psa-revision/common-mistakes/ - PSA format and marking: https://passthepsa.com/psa-revision/format-and-marking/ - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ Sources: BNF; BNF for Children; British Pharmacological Society and MSC Assessment PSA information. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # PSA study plan for 2, 4 and 8 weeks Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/study-plan/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: Plan PSA revision around daily BNF-open practice, a weekly error-log review and timed sets that build towards a full 120-minute paper. With 8 weeks, build foundations first; with 4, combine topics and timing; with 2, prioritise prescribing, high-risk medicines and your own error log. The final 48 hours are for consolidation, not new material. ## What principles apply to every PSA study plan? Every plan has the same four ingredients: daily practice with the BNF open, a running error log, timed work that builds towards a full paper, and rest before the exam. Only the amount of time at each stage changes. - Practise a little every day rather than a lot occasionally. - Weight your time towards prescribing, which carries the most marks in the paper. - Review your error log weekly and retest what you got wrong. - Do at least one full-length timed paper before the exam if time allows. Start by finding your baseline. Do a short mixed set with the BNF open in the first session, log what you got wrong, and let that result decide where the early weeks go. Someone who prescribes daily on the ward needs more work on exam technique and timing; someone who rarely prescribes needs more work on drug choice and the BNF layout. The paper has eight sections, 60 items and 200 marks over 120 minutes, and the prescribing section alone is worth 80 of the 200 marks. The plans below reflect that. ## What does an 8-week plan look like? Eight weeks allows foundations first, then volume, then timing. Spend the early weeks on method and the BNF layout, and keep timed work for the second half. Week | Focus | Activity --- | --- | --- 1 | BNF layout and prescription writing | Untimed items; learn the prescription format 2 | Prescribing and common drugs | Daily prescribing items; start the error log 3 | Prescription review and adverse reactions | Practise timing clues and interactions 4 | Monitoring and data interpretation | Link drugs to tests and results 5 | Calculations and planning management | Unit conversions; treatment summaries 6 | Mixed sets, first timed work | Timed sets of 10 items; review the log 7 | Weak areas, full paper | One timed 120-minute paper; fix the errors 8 | Consolidate | Light mixed practice; error-log retesting Treat weeks 6 to 8 as fixed. If earlier weeks overrun, shorten the topic work rather than the timed practice, because the exam rewards speed with the BNF as much as knowledge. ## What does a 4-week plan look like? Four weeks means combining topic work with timing from the start. Cover each section style once, then spend the second half on mixed timed sets. Week | Focus | Activity --- | --- | --- 1 | Prescribing and prescription writing | Daily items with the BNF; start the error log 2 | Review, reactions, monitoring and interactions | Short sets across styles; learn high-risk medicines 3 | Calculations, data and planning | Mixed timed sets; error-log review 4 | Full paper and consolidation | One timed paper, then targeted fixes and rest ## What can I achieve in a 2-week plan? Two weeks is enough to learn the method and fix your biggest weaknesses, not to cover everything. Prioritise ruthlessly and keep practising with the BNF open every day. Week | Focus | Activity --- | --- | --- 1 | Prescribing, high-risk medicines, writing format | Daily mixed items with the BNF; log every error 2 | Timed mixed sets and weak areas | Timed sets; one full paper if possible; retest the log - Give prescribing the largest share of your time; it is 80 of the 200 marks. - Learn the safe prescription format until it is automatic. - Skip rare topics; return to your most frequent errors instead. If you can add a third week, use it for a second full paper. The aim of the final week is a calm, practised routine, not a larger volume of material. ## How should I structure each week? Use a repeating weekly rhythm so that revision stays manageable alongside clinical work. A simple pattern is enough. - Most days: 30 to 60 minutes of practice, BNF open. - One day: a longer timed set and an error-log review. - One day: rest or very light revision. Adjust the amount to your own timetable. Regular, shorter sessions are more effective than rare marathons. Protect the rest day. Spaced, regular practice consolidates better when it is not squeezed into every available hour, and tired practice produces careless writing errors that you then log for the wrong reason. ## What should I do in the last 48 hours? In the last 48 hours consolidate and rest; do not start new topics. Cramming new material late adds anxiety and little benefit in an open-book exam. - Read your error log and the prescription format one more time. - Do a short, untimed set to keep the BNF search habit warm. - Check your booking details and the exam arrangements, using the official PSA information. - Plan your arrival time and travel arrangements so nothing is left to the morning. - Sleep properly and eat normally the night before. Note: Doses: if you revise any doses in the final days, confirm them in the BNF rather than relying on memory. ## Check yourself - How much of the 200 marks sits in the prescribing section? - At what point in your plan will you first do a timed set? - When will you do a full 120-minute paper? - How often will you review your error log? - Which topics will you deprioritise if time is short? - What will you do, and not do, in the last 48 hours? ## Questions people ask Q: Is 2 weeks enough to revise for the PSA? A: It can be, for a candidate who already prescribes regularly. Focus on prescribing, the safe writing format, high-risk medicines and your own error log, and practise with the BNF open every day. Q: When should I do a full practice paper? A: Once you can use the BNF quickly, ideally at least several days before the exam, so that you have time to fix what it shows. Q: Should I revise on the day before the exam? A: Lightly, if at all. Reread your error log, keep calm and sleep well; new material at this stage rarely helps. Q: How long should each study session be? A: Thirty to sixty minutes is a sensible block for most people. Regular short sessions work better than occasional long ones. ## Related notes - How to revise for the PSA: https://passthepsa.com/psa-revision/how-to-revise/ - PSA format and marking: https://passthepsa.com/psa-revision/format-and-marking/ - Common PSA mistakes that cost marks: https://passthepsa.com/psa-revision/common-mistakes/ Sources: BNF; British Pharmacological Society and MSC Assessment PSA information. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # PSA format and marking Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/format-and-marking/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: The PSA is an online, open-book assessment of 60 items across 8 sections, worth 200 marks in 120 minutes. That is 2 minutes per item on average, or 36 seconds per mark. Prescribing is the largest section at 80 marks. Prescribing items score the drug and the written details separately, and the pass mark is set per paper by the provider. ## What is the format of the PSA? The PSA is a single online paper of 60 items and 200 marks, sat in 120 minutes. It has 8 sections, each testing a different prescribing skill, and the online BNF and BNF for Children are available throughout. - 60 items, 200 marks, 120 minutes. - Eight sections, using four answer formats. - Open-book for the BNF and BNF for Children. - Run in the UK by the British Pharmacological Society and MSC Assessment. Items are not all worth the same. A prescribing item is worth far more than a single-best-answer item, which is why time and effort should follow the marks. Each section tests a distinct skill. Prescribing is writing a safe prescription; prescription review is finding the culprit drug on a chart; planning management is choosing the next treatment step; communicating information is choosing the most important safety advice to give a patient; calculation skills is working out a dose or rate; adverse drug reactions is recognising and responding to harm from a drug; drug monitoring is knowing which tests a drug needs and when; and data interpretation is acting on results. ## How many items and marks are in each section? The eight sections add up to 60 items and 200 marks, and prescribing alone accounts for 80 of those marks. The table shows the items, marks per item and total for each. Section | Items | Marks per item | Section total --- | --- | --- | --- Prescribing | 8 | 10 | 80 Prescription review | 8 | 4 | 32 Planning management | 8 | 2 | 16 Communicating information | 6 | 2 | 12 Calculation skills | 8 | 2 | 16 Adverse drug reactions | 8 | 2 | 16 Drug monitoring | 8 | 2 | 16 Data interpretation | 6 | 2 | 12 Prescribing and prescription review together make up 112 of the 200 marks. Revision time should reflect that weighting without neglecting the 2-mark sections, which make up the rest. ## What are the item styles? Four answer formats are used across the eight sections. Knowing the style in advance removes surprises on the day. Style | Sections --- | --- Free-text prescription on the exam chart | Prescribing Tick one or two prescriptions on a medication list | Prescription review Single best answer from five | Planning management, communicating information, adverse drug reactions, drug monitoring, data interpretation Type a number in the stated unit | Calculation skills In single-best-answer items more than one option may be reasonable, so choose the best one for the patient described, using the details given. ## How does time work in the PSA? The exam allows 36 seconds per mark, because 120 minutes is 7,200 seconds and the paper carries 200 marks. Use the marks on each item as a guide to how long to spend. Item worth | Time at exam pace --- | --- 2 marks | About 72 seconds 4 marks | About 2 minutes 24 seconds 10 marks | About 6 minutes - Practise at this pace so that it feels normal on the day. - Do not spend 5 minutes on a 2-mark item. - Flag a difficult item, move on and return if time remains. Prescribing items are worth 10 marks each, so the 8 of them take roughly 48 minutes of the 120 at exam pace. The remaining time covers the other 52 items. ## How are prescribing items marked? Prescribing items are marked in two parts that score separately: the choice of drug, and the written details such as dose, route and frequency. You can score on one part and not the other. - Choosing the right drug earns marks even if the written details are flawed. - A correct drug with a flawed written prescription still earns the drug marks, but loses some or all of the written-prescription marks. - Partial credit exists, so write a complete answer rather than leaving it blank. - Writing two drugs in one answer rather than committing to one risks losing the marks. Prescription review items are different: they ask you to tick the prescription or prescriptions responsible for a described problem, so the marks follow the ticks, not the written detail. Read whether the item wants one tick or two. The detail of a mark scheme is set by the provider for each item, so read the instruction line carefully. It tells you which chart section the marks are on, and whether a duration or other detail is required. Note: Check the official PSA information for the current rules on marking and on resources, which the provider can update. ## What is the pass mark? The pass mark is set for each paper by the provider and is not a fixed number, so there is no single score to aim for. Aim to maximise your marks across all sections. Because papers can vary in difficulty, a fixed target taken from someone else's experience is unreliable. Check the official PSA information for how results are reported. ## Check yourself - How many items, marks and minutes does the paper have? - Which section carries the most marks, and how many? - How many seconds per mark are allowed? - How many minutes does a 10-mark prescribing item get at exam pace? - What are the two separately scored parts of a prescribing item? - Who sets the pass mark, and is it fixed? ## Questions people ask Q: How many questions are in the PSA? A: There are 60 items across 8 sections, worth 200 marks in total, to be completed in 120 minutes. Q: Which PSA section is worth the most marks? A: Prescribing, with 8 items at 10 marks each, so 80 of the 200 marks. Prescription review is next at 32 marks. Q: Is there negative marking in the PSA? A: Check the official PSA information for the current marking rules. Check the official PSA information for the current marking rules. Leaving an item blank scores nothing, so give your best answer to every item. Q: What is the PSA pass mark? A: It is set for each paper by the provider and is not a fixed figure, so check the official PSA information for how it is determined. ## Related notes - How to revise for the PSA: https://passthepsa.com/psa-revision/how-to-revise/ - PSA study plan for 2, 4 and 8 weeks: https://passthepsa.com/psa-revision/study-plan/ - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ - Common PSA mistakes that cost marks: https://passthepsa.com/psa-revision/common-mistakes/ Sources: British Pharmacological Society and MSC Assessment PSA information; BNF. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # PSA revision FAQ Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/faq/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: The PSA is an online, open-book exam of 60 items, 200 marks and 120 minutes, with the BNF and BNF for Children available throughout. Many candidates revise for several weeks using BNF-open practice, an error log and timed sets. The pass mark is set per paper by the provider; check the official PSA information for rules on resits and resources. ## What is the exam, in brief? The PSA is a UK assessment of safe and effective prescribing, run by the British Pharmacological Society and MSC Assessment. It has 60 items in 8 sections, worth 200 marks, sat online in 120 minutes. The online BNF and BNF for Children are available throughout. The pass mark is set per paper by the provider and is not a fixed figure. ## How should I approach revision? Practise with the BNF open, attempt before you check, and record your errors. Timed work at 36 seconds per mark then builds the speed the exam needs. - Prescribing is the largest section at 80 of 200 marks. - Learn the high-risk medicines and the safe prescription format. - Look up doses and renal advice rather than memorising them. ## What about rules, resits and results? Rules on attempts, resits and results are set by the provider and can change, so check the official PSA information rather than relying on a revision site. The same applies to which resources are allowed beyond the BNF. ## Check yourself - How many items, marks and minutes are in the paper? - What is your plan for BNF-open practice this week? - How will you keep an error log? - When will you first do timed work? - Where will you check the official rules on resits and resources? ## Questions people ask Q: How long should I revise for the PSA? A: There is no fixed answer. Many candidates revise for several weeks, and plans of 2, 4 and 8 weeks all work if they include daily BNF-open practice, an error log and timed sets. Start earlier if you rarely prescribe. Q: Is the PSA open book? A: Yes for the BNF: the online BNF and BNF for Children are available throughout. Check the official PSA information for any other resources that are or are not provided. Q: What resources should I use to revise? A: The BNF and BNF for Children above all, because they are the tools you will use in the exam. Add original revision notes and practice items, and NICE guidance and Resuscitation Council UK guidance for the topics they cover. Q: How many practice questions should I do? A: There is no magic number. Quality matters more than volume: check each item against the BNF and log your errors. Cover all eight sections and do some timed sets and a full paper. Q: How is the PSA structured? A: There are 60 items in 8 sections, worth 200 marks, in 120 minutes. Prescribing has 8 items at 10 marks each, and the other sections have items worth 2 or 4 marks. Q: How much time do I get per question? A: On average 2 minutes per item, or 36 seconds per mark. A 2-mark item gets about 72 seconds, and a 10-mark prescribing item about 6 minutes. Q: What is the PSA pass mark? A: The pass mark is set for each paper by the provider and is not fixed. Do not rely on a figure quoted elsewhere; check the official PSA information. Q: Can I resit the PSA? A: Rules on resits and the number of attempts are set by the provider and by your medical school or employer, so check the official PSA information and ask them. Q: Do I need to memorise doses? A: Not in general, since the BNF is available. Know what to look up and where. Learn the high-risk medicines, the safe way to write a prescription and basic calculation methods. Q: What are the commonest ways to lose marks? A: Unsafe units and decimals, giving a volume instead of a dose, a missing frequency, the wrong chart section, ignoring renal function or allergy, and poor timing. Q: How should I prepare in the final two days? A: Consolidate, do not cram. Reread your error log, do a short untimed set, check the exam arrangements and get a proper night's sleep. Q: Which section should I prioritise? A: Prescribing carries 80 of the 200 marks, and prescription review a further 32, so give them the largest share of time while still covering the 2-mark sections. ## Related notes - How to revise for the PSA: https://passthepsa.com/psa-revision/how-to-revise/ - PSA study plan for 2, 4 and 8 weeks: https://passthepsa.com/psa-revision/study-plan/ - PSA format and marking: https://passthepsa.com/psa-revision/format-and-marking/ - Common PSA mistakes that cost marks: https://passthepsa.com/psa-revision/common-mistakes/ Sources: British Pharmacological Society and MSC Assessment PSA information; BNF. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # How to write a safe prescription Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/prescribing-safely/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: A safe prescription names the drug generically and states the dose in a clear unit, the route, the frequency and, where relevant, the duration or stop date. As-required prescriptions also need an indication and a maximum dose in 24 hours. Check allergies, weight and renal function first, and confirm everything against the BNF. ## What are the elements of a prescription? Every prescription must let someone else give the right drug, in the right amount, by the right route, at the right time. Each missing element is a point where an error can occur. 1. Drug name, written generically. 2. Dose, with a clear unit. 3. Route. 4. Frequency, or the instruction that it is once only. 5. Indication and maximum dose, if as required. 6. Duration or stop date, where relevant. 7. Signature and date, as the chart requires. In the PSA the written part of a prescribing item is marked separately from the drug choice, so the written elements carry marks. ## How should I write names and units? Use the generic name and write units in full where the BNF advises. Brand names can lead to duplication, and unclear units lead to tenfold and thousandfold errors. - Use generic names, for example paracetamol rather than a brand. - Write micrograms, nanograms and units in full, not abbreviated. - Write 500 mg rather than 0.5 g, and 100 micrograms rather than 0.1 mg. - Where a decimal is unavoidable, use a leading zero (0.5 mL, not .5 mL) and never a trailing zero (5 mg, not 5.0 mg). - State the dose as an amount of drug, not a volume of liquid. Where a drug has more than one salt or formulation, and the BNF distinguishes them, name the one you intend. ## How do I choose and write the route and frequency? Choose a route the drug can actually be given by and the patient can use, and state a frequency in the chart's own words. A blank frequency is marked as wrong. - Check the BNF medicinal forms if unsure that a route exists for the drug. - Use standard route abbreviations where the chart accepts them, or write the route in full. - Write the frequency clearly, for example once daily, twice daily or every set number of hours. - Take extra care with drugs given weekly or on alternate days, and write that explicitly. Think about the patient too: a patient who is vomiting or nil by mouth may not be able to take an oral drug. ## What is the difference between regular, once-only and as-required? The three sections of the chart are different forms and the instruction line tells you which one is wanted. Writing the right drug in the wrong form loses marks. Type | Needs | Example use --- | --- | --- Regular | Dose, route, frequency, duration if relevant | Ongoing treatment Once-only | Dose, route, date and time | A single immediate dose As required | Dose, route, minimum interval, maximum in 24 hours, indication | Symptom control such as pain or nausea An as-required prescription without an indication and a maximum dose in 24 hours is incomplete. Without a limit, repeated doses can add up beyond the safe total. ## When does a prescription need a duration or stop date? Write a duration or stop date whenever the treatment is meant to be short, and a review date where it should be revisited. Open-ended courses of some drugs cause harm. - Short courses of antibiotics should have a stated duration or review date. - Short courses of other drugs, such as steroids for an acute problem, need a clear stop. - Check the item's wording for whether a duration is required. If the question states a duration, include it; if the BNF gives a standard course length for the indication, use that. ## What should I check before prescribing? Check the patient before the drug: allergies, weight, renal function, pregnancy and current medicines. These details change the choice or the dose. - Allergy: avoid the drug and cross-reacting classes. - Weight: use it for weight-based doses, especially in children. - Renal function: look up the BNF renal impairment advice; some drugs need a dose change or avoidance. - Pregnancy and breastfeeding: check the BNF for suitability. - Other medicines: check interactions. For renal dosing, the BNF indicates whether eGFR or creatinine clearance should guide the dose; follow what the monograph says. ## What should I know about controlled drugs? Controlled drugs have additional legal requirements for prescriptions, and the BNF has a section setting these out. At exam level, know that they exist and write the prescription with extra care. - Expect stricter prescription-writing rules than for ordinary drugs. - Take particular care with opioids: dose, unit, route and frequency must be exact. - Use the BNF guidance rather than recall for any specific requirement. Note: Doses: this page teaches the structure of a prescription, not doses. Confirm every dose, route and frequency in the BNF. ## Check yourself - What are the seven elements of a prescription? - Why do you write 0.5 mL but 5 mg? - What two extra elements does an as-required prescription need? - How does a once-only prescription differ from a regular one? - When do you add a stop date? - Which patient details do you check before choosing a dose? ## Questions people ask Q: Why use generic names in prescriptions? A: Generic names avoid confusion between brands and reduce the risk of giving the same drug twice under different names. Use the BNF name unless the BNF says a brand matters. Q: What does an as-required prescription need? A: A dose, a route, a minimum interval or frequency, a maximum dose in 24 hours and an indication. Without a limit it is incomplete. Q: Do I need a stop date for every prescription? A: No. Add one, or a review date, where treatment is meant to be short, such as many antibiotic courses. Follow the wording of the item. Q: What is the difference between once-only and regular prescribing? A: A once-only prescription gives one dose at a stated time. A regular prescription repeats on a schedule. Writing one in the other's section can lose marks. ## Related notes - Common PSA mistakes that cost marks: https://passthepsa.com/psa-revision/common-mistakes/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ - PSA format and marking: https://passthepsa.com/psa-revision/format-and-marking/ - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ Sources: BNF guidance on prescription writing; BNF; NICE guidance on antimicrobial prescribing. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Common PSA mistakes that cost marks Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/common-mistakes/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: The most common PSA mistakes are writing units wrongly or abbreviating micrograms, nanograms and units, unsafe decimals such as trailing zeros, ambiguous abbreviations and frequencies, giving a volume instead of a dose, using the wrong chart section, ignoring renal function or allergy, not using the BNF, and poor time management. Each is avoidable with a fixed writing routine. ## Which unit and decimal errors lose marks? Unit and decimal errors are the easiest to make and the most dangerous in practice, because a misread number can cause a tenfold or thousandfold error. Use a fixed routine every time. - Write micrograms and nanograms in full; do not use mcg, ug or ng. - Write units in full; a handwritten U can be misread as a zero. - Do not add a trailing zero: write 5 mg, not 5.0 mg, which can be read as 50 mg. - Where a decimal is unavoidable, add a leading zero: write 0.5 mL, not .5 mL, which can be read as 5 mL. - Prefer the smaller unit to a decimal: 500 mg, not 0.5 g; 100 micrograms, not 0.1 mg. These conventions follow the BNF guidance on prescription writing. Read that section once and apply it every time. Practise writing doses by hand or on screen until the safe forms feel automatic. Under time pressure you revert to habits, so the habit has to be the safe one. ## Which abbreviations and frequencies cause trouble? Use only abbreviations that are standard and unambiguous, and write the frequency so that nobody can misread it. An unclear frequency may be marked as wrong. Ambiguity is the common thread. The test is whether a nurse who has never met the patient could give the drug exactly as intended without having to ask you. - Do not leave the frequency blank when the question requires one. - Avoid non-standard shorthand for drug names; use the generic name in full. - State once daily, twice daily or a stated number of hours apart in a form the chart accepts. - For a weekly drug, make the day or the word weekly explicit. - Where the form accepts a route abbreviation, use the standard one; if in doubt, write the route in full. Some drugs are given weekly or less often than daily, and a daily frequency written for them is a serious error. Check the BNF entry when a frequency looks unusual. ## What goes wrong with volumes and chart sections? A prescription states the amount of drug, not the volume of liquid. Writing 2 mL without a strength leaves the dose unclear and loses the marks. - Write the dose in mass or units (for example mg, micrograms or units), then the form if needed. - For an infusion, state the drug, the amount and the diluent or rate as the item requires. - Write a once-only drug in the once-only section, a regular drug in the regular section, and an as-required drug in the as-required section. - Read the instruction line, because it tells you which section the marks are on. A right drug in the wrong section can lose the prescription marks even though the choice was correct. ## How do ignored patient details cost marks? The case gives you the details that change the answer, and skipping them is a classic trap. Check them before you write anything. Detail | What to check --- | --- Allergy | Does the drug or its class match the allergy? Renal function | Does the BNF advise a dose change or avoidance? Weight, age | Is the dose weight-based or age-banded? Pregnancy, breastfeeding | Is the drug unsuitable or does it need caution? Other medicines | Is there an interaction that changes the choice? Underline the patient details in the stem before opening the BNF. Renal function matters most for drugs cleared by the kidney, and the BNF monograph states when to adjust or avoid. Allergy matters for the drug and for related drugs in the same class, so check cross-reactivity as well as the named drug. ## Which exam-technique mistakes cost marks? Technique errors cost marks even when knowledge is sound. The main ones are not using the BNF and poor time management. - Answering from memory when the BNF is open; check dose, route and indication every time. - Taking the first dose listed rather than the dose for the stated indication. - Spending too long on a 2-mark item and rushing the 10-mark prescribing items. - Leaving answers blank; on a prescribing item partial credit exists. - Hedging by writing two drugs, which risks losing the box. Note: Doses: the examples above are about format only. Confirm every dose in the BNF. Log these in your error log with their cause. A look-up failure needs BNF practice, a writing error needs rehearsal of the prescription format, and a time error needs timed sets. Fixing the cause is faster than relearning the topic. ## Check yourself - How should micrograms, nanograms and units be written? - Why is 5.0 mg unsafe, and why is .5 mL unsafe? - Why is 2 mL not a dose? - What happens if a regular drug goes in the once-only section? - Which patient details should you check before writing any prescription? - How long should a 2-mark item take at exam pace? ## Questions people ask Q: Why must micrograms be written in full? A: Abbreviations such as mcg or ug can be misread as mg, which is a thousandfold error. The BNF advises writing micrograms and nanograms in full. Q: What is the safest way to write a decimal dose? A: Add a leading zero (0.5 mg, not .5 mg) and avoid trailing zeros (5 mg, not 5.0 mg). Where possible use the smaller unit instead of a decimal. Q: Can I lose marks for using the wrong chart section? A: Yes. A once-only drug written as a regular prescription, or the reverse, can lose the prescription marks even when the drug is right. Q: Should I always use the BNF even when I think I know the answer? A: Yes. It is available throughout, and a quick check of dose, route and patient modifiers catches errors that recall misses. ## Related notes - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ - How to revise for the PSA: https://passthepsa.com/psa-revision/how-to-revise/ - PSA format and marking: https://passthepsa.com/psa-revision/format-and-marking/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ Sources: BNF guidance on prescription writing; BNF. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # PSA calculation skills: doses, rates and units Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/calculations/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: PSA calculation items reward a fixed routine: read the units, identify the target (one dose, daily dose, volume or rate), calculate in the preparation's units, convert, then check the magnitude. Learn the ladder (1 g = 1000 mg = 1,000,000 micrograms), that 1% is 10 mg/mL and 1 in 1000 is 1 mg/mL, and that rate equals volume divided by time. ## What is the unit conversion ladder? Each step down the ladder multiplies by 1000 and each step up divides by 1000. Most thousandfold errors come from moving the wrong way, or from skipping a step. Unit | Equals | Example --- | --- | --- 1 g | 1000 mg | 0.5 g = 500 mg 1 mg | 1000 micrograms | 0.25 mg = 250 micrograms 1 microgram | 1000 nanograms | 62.5 micrograms = 62,500 nanograms 1 litre | 1000 mL | 0.25 litre = 250 mL Write micrograms, nanograms and units in full on a prescription. Abbreviations such as mcg, ng and U are easily misread and are discouraged in the BNF. ## How do percentage and ratio strengths convert to mg per mL? A percentage strength means grams per 100 mL, so multiply the percentage by 10 to get mg per mL. Strength | Meaning | Concentration --- | --- | --- 1% | 1 g in 100 mL | 10 mg/mL 2% | 2 g in 100 mL | 20 mg/mL 1 in 1000 | 1 g in 1000 mL | 1 mg/mL 1 in 10 000 | 1 g in 10 000 mL | 0.1 mg/mL (100 micrograms/mL) Units (insulin, heparin) are a measure of biological activity, not mass, and cannot be converted to milligrams. Read the strength on the label, for example units per mL, and work from that. ## Which weight do I use for mg/kg doses? Use the weight given in the question unless the BNF or the item says otherwise. - Adults: actual body weight is the default. Some drugs and local protocols use ideal or adjusted weight in obesity, and many have a maximum dose. Check the BNF. - Children: use current weight, and do not exceed the adult dose. Some doses are by age band or body surface area (mg/m2) instead. - Per dose or per day? A dose per kg per day must be divided by the number of doses before you convert to a volume. - Dose divided by concentration gives volume. ## How do I calculate infusion rates and drops per minute? Rate in mL per hour is volume in mL divided by time in hours. - Drops per minute = volume (mL) x drop factor (drops per mL) / time (minutes). The giving set's drop factor will be stated in the question. - Syringe pumps: concentration is drug per mL, so rate (mL/hour) = prescribed dose per hour / concentration per mL. - Make sure the drug amount and the dose rate are in the same unit before dividing. ## How do I calculate BMI and creatinine clearance? BMI is weight in kg divided by height in metres squared. Cockcroft-Gault creatinine clearance in mL/min = (140 - age in years) x weight in kg x constant, divided by serum creatinine in micromol/L. The constant is 1.23 for men and 1.04 for women. - eGFR is reported by the laboratory in mL/min/1.73 m2 and suits most adult dosing decisions. - The BNF advises creatinine clearance for older people, extremes of body weight and drugs with a narrow margin of safety that are renally cleared. DOAC dosing is based on creatinine clearance. - In obesity, malnutrition or oedema the weight you enter changes the answer. Check the BNF. ## Worked examples All figures below are invented for practice. 1. Adrenaline 1 in 1000, 500 micrograms IM. 1 in 1000 is 1 mg/mL. 500 micrograms = 0.5 mg. Volume = 0.5 mg / 1 mg per mL = 0.5 mL. 2. How many mg are in 5 mL of a 2% solution? 2% = 20 mg/mL. 5 x 20 = 100 mg. 3. A child weighs 12 kg and is prescribed 30 mg/kg/day in 3 divided doses, using a suspension of 250 mg in 5 mL. Daily dose = 12 x 30 = 360 mg. Each dose = 360 / 3 = 120 mg. Strength = 250 / 5 = 50 mg/mL. Volume = 120 / 50 = 2.4 mL. 4. 1000 mL over 8 hours. Rate = 1000 / 8 = 125 mL/hour. With a 20 drops/mL set: 125 x 20 = 2500 drops per hour; 2500 / 60 = 41.7, so about 42 drops per minute. 5. Heparin 25,000 units in 50 mL = 500 units/mL. Prescribed 1000 units/hour: 1000 / 500 = 2 mL/hour. 6. Dilution: 5 mL of 10 mg/mL contains 50 mg. Made up to 50 mL, concentration = 50 / 50 = 1 mg/mL. 7. BMI for 85 kg and 1.70 m. Height squared = 2.89. 85 / 2.89 = 29.4 kg/m2. 8. Creatinine clearance, man aged 70, 80 kg, creatinine 100 micromol/L. (140 - 70) = 70. 70 x 80 = 5600. 5600 x 1.23 = 6888. 6888 / 100 = 68.9, about 69 mL/min. For a woman with the same values: 5600 x 1.04 = 5824; 5824 / 100 = 58 mL/min. Note: Confirm in the BNF: these examples use invented numbers to teach arithmetic. Check every dose, maximum and preparation strength in the BNF, which is available throughout the exam. ## What checking routine catches calculation errors? Check the answer against what a real patient would receive before you type it. 1. Write down the units asked for in the answer box. 2. Confirm the target: one dose, daily dose, volume or rate. 3. Carry full figures through and round once, at the end. 4. Ask whether the answer is plausible: would a nurse draw up that volume, and would that rate empty the bag in a sensible time? 5. If the answer is ten or a hundred times too big or small, recheck the decimal point and the unit ladder. ## Check yourself - How many micrograms are in 0.75 mg? - What concentration in mg/mL is a 0.5% solution? - What does 1 in 10 000 mean in mg/mL? - A daily dose is given in 4 divided doses. What is the single dose? - How do you turn a dose in mg and a strength in mg/mL into a volume? - What is the rate in mL/hour for 500 mL over 5 hours? - Which constant is used for women in Cockcroft-Gault? - Why can units of insulin not be converted to mg? ## Questions people ask Q: Should I write mcg or micrograms? A: Write micrograms in full, and nanograms and units in full too. Abbreviations are easily misread, and a micrograms-to-milligrams slip is a thousandfold error. Q: How do I convert 1 in 1000 to mg per mL? A: 1 in 1000 means 1 g in 1000 mL, which is 1000 mg in 1000 mL, so 1 mg/mL. A 1 in 10 000 solution is 0.1 mg/mL. Q: What is the Cockcroft-Gault formula? A: Creatinine clearance in mL/min = (140 - age) x weight in kg x 1.23 for men or 1.04 for women, divided by serum creatinine in micromol/L. Q: Is eGFR the same as creatinine clearance? A: No. eGFR is standardised to 1.73 m2 body surface area, while Cockcroft-Gault uses the patient's own weight. The BNF indicates when creatinine clearance is preferred. ## Related notes - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ - Emergency prescribing for the PSA: https://passthepsa.com/psa-revision/emergency-prescribing/ - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ Sources: BNF; BNF for Children; NICE guidance on obesity and BMI. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # PSA communicating information: counselling points Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/communicating-information/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: The PSA communicating information items ask you to choose the single most important thing a patient needs to know about a medicine. Use a method: indication, how to take it, key risk, and what to do if something goes wrong. Rank by harm prevented, and prefer advice specific to that drug over generic advice. ## What does the communicating information skill test? The item tests prioritisation: several options may be true, but one prevents the most serious harm. - Rank by harm, not by how often a side effect occurs. - Specific beats general: a drug-specific warning usually beats advice that applies to any medicine. - Fit the patient: pregnancy, driving, occupation and other medicines change which point matters most. ## What method picks the right counselling point? 1. Indication: say what the medicine is for, so the patient knows why to take it. 2. How to take it: dose timing, route, relation to food, and technique. 3. Key risk: the worst realistic harm, and the sign that should prompt action. 4. If something goes wrong: what to do for missed doses, vomiting, illness or symptoms, and who to contact. The BNF monograph sections on important safety information and patient and carer advice list the points the exam favours. ## What are the key counselling points for cardiovascular and anticoagulant drugs? Medicine | Most important point | Why --- | --- | --- Warfarin | Keep INR checks; report bleeding; tell staff before any new medicine, including antibiotics and OTC drugs | Many interactions alter INR DOACs | Take regularly without missed doses; carry the alert card; report bleeding; do not stop without advice | Short half-life gives little protection if doses are missed GTN | Sit down to use it; if chest pain is not relieved within the time given in the patient advice (about 5 minutes), call 999; never with sildenafil-type (PDE5 inhibitor) drugs | Hypotension; profound hypotension with PDE5 inhibitors Statins | Report unexplained muscle pain or weakness | Myopathy and rhabdomyolysis ## What are the key counselling points for inhalers, steroids and diabetes drugs? Medicine | Most important point | Why --- | --- | --- Inhalers and spacers | Preventer is taken daily even when well, unless on a combined maintenance-and-reliever regimen where the prescriber explains the single inhaler; reliever is for symptoms; use a spacer with a metered-dose inhaler, one puff at a time; rinse the mouth after an inhaled steroid | Poor technique and reliever overuse mark poor control Oral steroids | Carry a steroid card; do not stop suddenly after a long course; seek advice when ill (sick-day rules) | Adrenal suppression can cause crisis Metformin | Temporarily stop during dehydrating illness and restart once eating and drinking normally, seeking advice if unsure; for iodinated contrast follow local policy (usually withheld only if eGFR is low or there is acute kidney injury) | Risk of lactic acidosis with acute kidney injury Insulin | Recognise and treat hypoglycaemia and carry fast-acting carbohydrate; do not stop insulin when ill, and check glucose (and ketones in type 1) more often; follow DVLA driving advice | Hypoglycaemia is the main harm of treatment; omitting insulin when ill risks diabetic ketoacidosis Bisphosphonates (oral) | Swallow whole with a full glass of plain water on an empty stomach; stay upright and wait before food, drink or other medicines (at least 30 minutes, longer for ibandronate) | Oesophageal irritation ## What are the key counselling points for opioids, antidepressants, methotrexate and antibiotics? Medicine | Most important point | Why --- | --- | --- Opioids | Expect constipation and take a regular laxative; drowsiness, driving and alcohol; do not stop abruptly after regular use, and discuss dependence and dose reduction with the prescriber | Constipation is very common and does not wear off; sedation and respiratory depression are the key risks Methotrexate | ONCE WEEKLY, never daily; report sore throat, fever, mouth ulcers, bruising or breathlessness | Daily dosing errors can be fatal; bone marrow toxicity Antidepressants | Effect takes weeks; do not stop suddenly; report worsening mood or agitation early on | Discontinuation symptoms; early risk review Antibiotics | Take as prescribed; report severe or persistent diarrhoea; drug-specific warnings (alcohol with metronidazole, upright with doxycycline) | Prevents harm and failure of treatment Rifampicin | Orange body fluids; reduces the effect of pills, patch, ring and implant (not injectable, IUS or copper IUD), so alternative contraception advice is needed | Enzyme induction ## How are contraception and teratogens counselled? Contraception counselling at PSA level covers missed pills, interacting drugs and when to seek help; check FSRH guidance for the exact rules. - Missed combined pills: one missed pill (taken 24 hours or more late) should be taken as soon as remembered, with no extra precautions; two or more missed pills reduce protection, so take the most recent missed pill, use condoms or abstain for 7 days, and consider emergency contraception depending on where in the pack the pills were missed and whether sex has occurred. Check FSRH guidance. - Enzyme inducers, such as rifampicin, carbamazepine and St John's wort, reduce hormonal contraceptive effect. - Valproate: enrolled in a Pregnancy Prevention Programme because of major malformations and neurodevelopmental harm; not for women and girls who can become pregnant unless conditions are met. - Isotretinoin: strictly contraindicated in pregnancy, with a Pregnancy Prevention Programme and effective contraception. - Topiramate, acitretin and mycophenolate also carry pregnancy-prevention requirements; check the BNF and MHRA advice. - ACE inhibitors and ARBs: avoid in pregnancy unless essential, because of fetal and neonatal renal harm (mainly second and third trimesters); advise review when planning a pregnancy. Note: Confirm in the BNF: counselling points here are principles, not doses. Check the BNF patient advice, important safety information and FSRH guidance before relying on them. ## Check yourself - What is the single most important counselling point for methotrexate? - What advice should a patient on long-term oral steroids receive? - How should oral bisphosphonates be taken? - What is the key counselling point for GTN, and which drug class must not be combined with it? - Why should insulin never be stopped during illness? - What constipation advice goes with opioids? - Which medicines need a Pregnancy Prevention Programme? - What four-step method organises counselling? ## Questions people ask Q: What does the communicating information section ask? A: It asks you to choose the single most important thing a patient should be told about a medicine. Several options may be true, so you rank them by the harm they prevent. Q: What should patients on oral steroids be told? A: Carry a steroid card, do not stop suddenly after prolonged or repeated courses, and seek advice when unwell because extra doses may be needed. Check the BNF for specifics. Q: What is the key warning with methotrexate? A: It is taken once a week, never daily, and patients should report sore throat, fever, mouth ulcers, bruising or breathlessness promptly. Q: Which medicines carry pregnancy prevention programmes? A: Valproate, topiramate and oral retinoids such as isotretinoin and acitretin have Pregnancy Prevention Programmes because of serious fetal harm, and mycophenolate has similar mandatory measures. ACE inhibitors and ARBs have no such programme but are avoided in pregnancy. ## Related notes - Adverse drug reactions for the PSA: https://passthepsa.com/psa-revision/adverse-drug-reactions/ - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ - Antibiotic prescribing for the PSA: https://passthepsa.com/psa-revision/antibiotics/ Sources: BNF; MHRA Drug Safety Update; FSRH guidance on contraception; NICE guidance. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # High-risk medicines for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/high-risk-medicines/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: High-risk medicines are drugs where an ordinary error causes severe harm: anticoagulants, insulin, opioids, methotrexate, potassium and other concentrated electrolytes, digoxin, lithium, aminoglycosides, and vinca alkaloids. For each, the PSA rewards one specific safeguard: check renal function and weight, write units and days in full, use only the licensed route, and arrange the monitoring. ## What makes a medicine high-risk? A medicine is high-risk when a small, common error produces serious or fatal harm. The same few features recur, and recognising the feature tells you the safeguard the exam wants. - Narrow therapeutic index: the effective and toxic doses are close (digoxin, lithium, aminoglycosides, warfarin). - Dose depends on a patient factor: weight, renal function or age (LMWH, DOACs, gentamicin, IV paracetamol). - Unit or frequency confusion: units, micrograms versus milligrams, weekly versus daily (insulin, methotrexate). - Wrong-route or wrong-dilution risk: concentrated potassium, vinca alkaloids. - Needs monitoring after the first prescription: INR, levels, U&E. In the PSA the question is usually not which drug, but what makes this prescription safe. Look for the patient factor the case supplies, such as a low eGFR, a low body weight or an interacting new drug. ## High-risk medicines: hazard and safe-prescribing rule Drug | Main hazard | The rule --- | --- | --- Warfarin | Bleeding; INR changes with interactions | Indication-specific INR target; check INR after any new interacting drug DOACs | Bleeding if the drug accumulates | Dose by indication and creatinine clearance; check renal function LMWH | Bleeding; accumulation in renal impairment | Dose by weight and renal function; check platelets if prolonged Insulin | Hypoglycaemia; tenfold errors | Write units in full; use an insulin syringe or pen; never stop basal insulin in type 1 diabetes Opioids | Respiratory depression; constipation | Start low in opioid-naive patients; co-prescribe a laxative; reduce in renal impairment Methotrexate (oral, inflammatory disease) | Marrow suppression from daily dosing | Once WEEKLY; write the day; one strength of tablet Potassium (IV) | Cardiac arrest if given too fast or undiluted | Premixed bags; never a bolus; rate limits and U&E monitoring Digoxin | Toxicity: arrhythmia, nausea, visual change | Lower dose in renal impairment; correct potassium; level at least 6 hours post dose Lithium | Toxicity with dehydration or interacting drugs | Prescribe by brand; level 12 hours post dose; avoid NSAIDs; ACE inhibitors, ARBs and thiazides raise levels, so avoid or monitor levels closely Aminoglycosides | Nephrotoxicity and ototoxicity | Dose by weight; levels and renal function; shortest course Vinca alkaloids | Fatal if given intrathecally | Intravenous only; never by any other route IV paracetamol | Hepatotoxicity from overdose; mg versus mL error | Prescribe in mg and state the volume; weight-based under 50 kg; lower maximum daily dose if risk factors ## How do you prescribe anticoagulants safely? Anticoagulant safety starts with a bleeding-risk and renal-function check before the first dose. Each class then has its own trap. - Warfarin: the INR target depends on the indication, and many antibiotics, azoles and amiodarone raise the INR. Vitamin K and prothrombin complex concentrate are used for serious bleeding. - DOACs: choice and dose depend on the indication and on creatinine clearance (Cockcroft-Gault), not eGFR. Dabigatran is the most dependent on renal excretion. Idarucizumab reverses dabigatran; other DOACs have their own reversal routes in local guidance. - LMWH: dose by weight for treatment and adjust in renal impairment. Unfractionated heparin is monitored by APTT and is reversed by protamine. - Combined antiplatelet and anticoagulant use raises bleeding risk and needs a clear indication. ## Insulin, opioids and controlled drugs: what are the rules? Insulin must always be prescribed with the word units written in full. U or IU can be misread as a number, and an ordinary syringe must never be used to draw up insulin. - Name the product and the device. Never draw up insulin from a pen or cartridge with a syringe. - Only soluble (short-acting) insulin is given intravenously. - Type 1 diabetes needs basal insulin continued even when not eating, to avoid ketoacidosis. Opioids need a start-low approach in opioid-naive and elderly patients, a regular laxative, and a lower dose or a different opioid in renal impairment because morphine metabolites accumulate. Immediate-release and modified-release morphine are different products: name the formulation. Naloxone reverses respiratory depression, but its action is shorter than that of many opioids, so observation continues. Controlled drugs have extra prescribing rules. A Schedule 2 or 3 prescription for the community must state the dose, the form and (where appropriate) the strength, and the total quantity or number of dose units in both words and figures. Check the BNF for the schedule of a drug and local policy for ward practice. ## Which drugs have a weekly dose or a never-route? Oral methotrexate for inflammatory disease is taken once a week, and a daily prescription is a recognised cause of fatal marrow suppression. Write the day of the week in the prescription, prescribe one tablet strength, and arrange blood monitoring. Folic acid is usually given on a different day from the methotrexate. Concentrated potassium chloride must be diluted before use and never given as an intravenous bolus. Prefer ready-made infusion bags, set a maximum infusion rate according to local policy and check U&E. Do not give it to a patient with hyperkalaemia or severe renal impairment without senior advice. Vinca alkaloids such as vincristine are given by intravenous infusion only. Intrathecal administration is fatal, so these drugs are supplied and labelled to prevent a spinal route. Intrathecal chemotherapy is restricted to trained staff under strict local procedures. IV paracetamol is prescribed in milligrams, with the volume stated, never as a volume alone. The maximum for adults over 50 kg is 4 g in 24 hours. Under 50 kg, dose by weight. In adults of 50 kg or more with risk factors such as malnutrition, chronic alcohol use, dehydration or liver disease, a lower maximum daily dose applies; check the BNF. Note: Check doses: confirm all doses, rate limits and renal adjustments in the BNF or local guidance before writing them. ## Which narrow-therapeutic-index drugs need levels? Digoxin, lithium and aminoglycosides are prescribed with a plan for levels and renal function. Digoxin toxicity is more likely with hypokalaemia, renal impairment and interacting drugs such as amiodarone, verapamil and clarithromycin, so the dose is reduced or the interaction avoided. Lithium is prescribed by brand because formulations differ in bioavailability. Dehydration, new NSAIDs, ACE inhibitors, ARBs and thiazides raise lithium levels. Gentamicin is dosed by weight, usually once daily, with a level and renal function checked according to the local protocol. ## Check yourself - Which two patient factors most often change a DOAC dose? - How should insulin be written on a chart, and which syringe is used? - What is the frequency rule for oral methotrexate, and what is the classic error? - Why is a concentrated potassium ampoule never given as a bolus? - Which drugs raise lithium levels? - When is a digoxin level taken relative to the dose? - Which route is fatal for vincristine? - How does IV paracetamol dosing change under 50 kg? ## Questions people ask Q: What are the highest-risk medicines in the PSA? A: Anticoagulants, insulin, opioids, methotrexate, potassium, digoxin, lithium and aminoglycosides recur most often. Each has a standard safeguard that the exam expects you to apply. Q: How should insulin doses be written? A: Write the word units in full beside the number, never U or IU, and name the insulin product. Use an insulin syringe or pen, not an ordinary syringe. Q: Why is methotrexate a high-risk drug? A: Oral methotrexate for inflammatory disease is a weekly drug, and accidental daily dosing can cause fatal marrow suppression. Always state the day of the week. Q: Can potassium chloride be given as a bolus? A: No. Concentrated potassium chloride must be diluted and infused at a controlled rate, because rapid administration can cause cardiac arrest. Q: What is the maximum daily dose of paracetamol for adults? A: For adults over 50 kg it is 4 g in 24 hours. Use weight-based dosing under 50 kg, and a lower maximum daily dose where there are risk factors for liver injury (check the BNF). ## Related notes - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ Sources: BNF; NICE guidance on anticoagulants and diabetes; National Patient Safety Agency alerts on high-risk medicines; MHRA Drug Safety Update. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Drug monitoring for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/drug-monitoring/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: Drug monitoring means matching a drug to the toxicity or effect it needs checked: lithium levels with renal and thyroid function, INR for warfarin, FBC and liver tests for methotrexate, TFTs for amiodarone and levothyroxine, U&E for ACE inhibitors and diuretics, and neutrophils for clozapine. Take levels at the right time, usually pre-dose, or 12 hours post dose for lithium. ## How do you approach a monitoring question? Work from the main toxicity of the drug to the test that detects it. Ask what could go wrong, which organ is affected and which blood test or observation shows it early. - Narrow therapeutic index drugs need drug levels (lithium, gentamicin, vancomycin, ciclosporin, tacrolimus, sometimes phenytoin). - Drugs with end-organ toxicity need organ function tests (methotrexate, amiodarone, azathioprine). - Drugs that shift electrolytes or renal function need U&E (ACE inhibitors, ARBs, diuretics, spironolactone). - Drugs with a measurable effect need an effect test (warfarin with INR, levothyroxine with TSH). - Baseline tests are taken before starting, then repeated at intervals that are most frequent in the first weeks. The BNF monograph lists monitoring under the drug, and the BNF treatment summaries and NICE guidance give the intervals. Where an interval is not certain, check the BNF or the local shared-care protocol. ## Monitoring table: drug, test and reason Drug | Monitor | Why --- | --- | --- Lithium | Serum level, U&E/eGFR, TFT, calcium, weight | Narrow index; renal clearance; hypothyroidism and hyperparathyroidism Digoxin | Potassium, renal function; level if toxicity or non-adherence suspected | Toxicity rises with hypokalaemia and renal impairment Gentamicin | Level per local protocol, renal function | Nephrotoxic and ototoxic Vancomycin | Pre-dose (trough) level, renal function | Nephrotoxic; level guides dose Warfarin | INR | Dose response varies with diet, illness and interactions Methotrexate | FBC, LFT, renal function | Marrow, liver and renal toxicity Amiodarone | TFT, LFT, baseline chest X-ray, ECG | Thyroid, liver and lung toxicity ACE inhibitor or ARB | U&E before and 1-2 weeks after starting or increasing the dose | Hyperkalaemia and fall in renal function Loop and thiazide diuretics | Sodium, potassium, renal function | Hyponatraemia, hypokalaemia, volume depletion Statins | LFT at baseline and later; CK only if muscle symptoms | Hepatic effect; myopathy Azathioprine | TPMT status before starting; FBC; LFT | Low TPMT activity risks severe myelosuppression Clozapine | Neutrophil count: weekly at first, then less often | Agranulocytosis Levothyroxine | TSH 8-12 weeks after a dose change, then yearly when stable | Titrate to TSH; over-treatment causes AF and bone loss Ciclosporin, tacrolimus | Trough (pre-dose) level, renal function, BP, potassium | Narrow index; nephrotoxic Antipsychotics | Weight, BP, glucose or HbA1c, lipids, prolactin | Metabolic and endocrine effects ## When should a drug level be taken? A level is only interpretable if it is taken at the right time after the last dose. The rules below are the ones the exam expects. - Lithium: 12 hours after the last dose, once the patient is at steady state, which is about 5 to 7 days after a dose change. - Digoxin: at least 6 hours after the dose, because earlier samples reflect the distribution phase. Routine levels are not needed; take one when toxicity or non-adherence is suspected. - Gentamicin: a pre-dose (trough) or timed level as the local protocol states. Vancomycin: a pre-dose (trough) sample. - Ciclosporin and tacrolimus: trough, immediately before the next dose. - Phenytoin: levels guide dose changes because small increases can cause disproportionate rises; check albumin as it is highly protein-bound. Timing errors cause false conclusions: a lithium level taken 4 hours post dose will be falsely high, and a digoxin level taken 2 hours post dose will be falsely high. ## Which drugs need blood count, liver or thyroid monitoring? Methotrexate, azathioprine and clozapine are monitored for bone-marrow suppression. Methotrexate and azathioprine need FBC, LFT and renal function at baseline and regularly, with the patient taught to report sore throat, mouth ulcers, bruising or fever at once. Clozapine requires a neutrophil count before starting and at set intervals, and the registration and monitoring system must be followed. Amiodarone needs thyroid and liver tests at baseline and about every 6 months, with a baseline chest X-ray. Its effects persist for months after stopping because of its very long half-life. Levothyroxine is monitored with TSH once the patient is stable. Lithium and amiodarone both disturb thyroid function and are monitored with TFT. ## When is U&E monitoring needed? ACE inhibitors, ARBs, spironolactone and diuretics are monitored by U&E because they change potassium and renal function. Check U&E before starting and soon after each dose increase. A small rise in creatinine is expected after starting an ACE inhibitor. A large rise, or hyperkalaemia, needs the drug reviewed, and potassium-raising co-prescriptions should be stopped. Follow NICE and BNF guidance on thresholds. Statin monitoring is often misremembered. LFT is checked at baseline and later, but CK is measured only when the patient reports unexplained muscle pain, weakness or dark urine. Note: Check intervals: monitoring frequencies vary by drug and indication. Confirm intervals and target ranges in the BNF or local shared-care guidance. ## Check yourself - When is a lithium level taken, and why? - What is the minimum time after a digoxin dose before a level is taken? - Which blood tests are needed for methotrexate? - What does TPMT testing predict before azathioprine? - Which three organs does amiodarone threaten? - How is levothyroxine dosing monitored? - When is CK measured in a patient taking a statin? - Which drugs need a trough level? ## Questions people ask Q: When should a lithium level be taken? A: Take it 12 hours after the last dose, once steady state has been reached. A sample taken earlier will read falsely high. Q: What monitoring does amiodarone need? A: Thyroid and liver function at baseline and about every 6 months, and a baseline chest X-ray. Thyroid, liver, lung and eye effects are all possible. Q: Why is TPMT tested before azathioprine? A: Low or absent TPMT activity causes high levels of toxic metabolites and severe myelosuppression, so the dose is reduced or the drug avoided. Q: Do statins need routine CK monitoring? A: No. CK is measured only if the patient has unexplained muscle symptoms. Liver tests are checked at baseline and later. Q: What is a trough level? A: A trough is a sample taken just before the next dose, when the drug level is lowest. It is used for gentamicin, vancomycin, ciclosporin and tacrolimus. ## Related notes - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - Adverse drug reactions for the PSA: https://passthepsa.com/psa-revision/adverse-drug-reactions/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ Sources: BNF; NICE guidance on bipolar disorder, lipid modification and thyroid disease; MHRA Drug Safety Update; Shared-care protocols. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Renal dosing for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/renal-dosing/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: In renal impairment, check which measure of kidney function the BNF wants. eGFR is fine for most drugs, but creatinine clearance (Cockcroft-Gault) is preferred for DOACs, narrow-therapeutic-index and nephrotoxic drugs, and at extremes of age or body weight. Avoid or reduce renally cleared drugs, stop nephrotoxins in acute kidney injury, and use sick-day rules. ## eGFR or creatinine clearance: which should you use? Use eGFR for most drugs and creatinine clearance for the cases where precision matters. The eGFR reported by laboratories is standardised to a body surface area of 1.73 square metres, so it can over- or under-estimate the function of a small or large patient. The BNF recommends calculating creatinine clearance with the Cockcroft-Gault equation, using the weight the BNF specifies (usually actual body weight, but ideal or adjusted weight in obesity), in these situations: - Drugs with a narrow therapeutic index or that are nephrotoxic. - Older people, and patients at extremes of body weight. - DOACs, whose licensed dosing is written in terms of creatinine clearance. - Any drug where the monograph states creatinine clearance rather than eGFR. Creatinine itself is a poor guide in the frail and in low muscle mass, because a normal creatinine can hide a low clearance. Use the creatinine clearance, and check how the BNF band for that drug is expressed. ## Which drugs are nephrotoxic or harm the kidney? Nephrotoxic drugs either damage the kidney directly or reduce its perfusion, and they accumulate in patients with a low GFR. - NSAIDs: reduce renal blood flow, especially with an ACE inhibitor or ARB plus a diuretic. - ACE inhibitors, ARBs and diuretics: haemodynamic effects in volume depletion or renal artery stenosis. - Aminoglycosides, vancomycin and amphotericin. - Ciclosporin and tacrolimus. - Intravenous contrast agents. - Lithium: also causes nephrogenic diabetes insipidus. - Trimethoprim: raises serum creatinine without changing true GFR and can raise potassium. In acute kidney injury, stop or hold nephrotoxic and renally cleared drugs, review all prescriptions, and restart them according to recovery. ## Drugs to avoid or reduce in renal impairment Drug or class | Problem | What to do --- | --- | --- NSAIDs | Reduce renal perfusion; AKI | Avoid in significant impairment; avoid in AKI Metformin | Lactic acidosis risk | Avoid if eGFR below 30; review dose if eGFR below 45; stop in AKI DOACs | Accumulate; bleeding | Dose or avoid by creatinine clearance; dabigatran most renally cleared LMWH | Accumulates | Reduce dose or use unfractionated heparin in severe impairment Gabapentin and pregabalin | Excreted unchanged; sedation, confusion | Reduce dose by renal function Morphine | Active metabolites accumulate | Avoid or reduce; prefer opioids with less renal clearance per local palliative guidance Digoxin | Renally excreted; toxicity | Lower dose and levels; correct potassium Lithium | Renally excreted; toxicity | Avoid in severe impairment; specialist-managed Nitrofurantoin | Ineffective at low GFR; toxicity | Avoid below the BNF eGFR threshold Trimethoprim | Raises creatinine and potassium | Reduce dose in impairment; check potassium ## What are the sick-day rules? Sick-day rules tell patients to pause certain drugs during dehydrating illness such as vomiting, diarrhoea or fever. The aim is to prevent acute kidney injury, hyperkalaemia and lactic acidosis. The drugs to pause are often remembered as SADMANS: - Sulfonylureas (hypoglycaemia). - ACE inhibitors. - Diuretics. - Metformin. - ARBs. - NSAIDs. - SGLT2 inhibitors (ketoacidosis and volume depletion). Restart them after the patient has been eating and drinking normally for 24 to 48 hours. Patients on regular steroids need a different rule, because stopping them is dangerous, so they follow steroid sick-day guidance. ## Where do you find renal dosing in the BNF? Each drug monograph has a Renal impairment section that gives dose adjustments, usually by eGFR or creatinine clearance bands. Read the unit and the band before applying the adjustment. - Open the monograph and go to Renal impairment. - The guidance on prescribing in renal impairment in the BNF explains eGFR, creatinine clearance and the Cockcroft-Gault equation. - Check the Indications and dose section first, because adjustments differ between indications. - Look at Cautions and Contra-indications as well as the renal section. In the exam, pick the number the case gives, convert it to the unit the monograph uses, and then choose the band. Note: Check bands: renal thresholds change as guidance is updated. Confirm every threshold and adjustment in the current BNF. ## Check yourself - When should creatinine clearance be used instead of eGFR? - Why can a normal creatinine mislead in an older, thin patient? - What is the BNF threshold for stopping metformin, and what about review? - Which drug in the triple whammy is a diuretic, and what are the other two? - Why is morphine a poor choice in severe renal impairment? - What does SADMANS stand for? - When do patients restart sick-day drugs? - Where is renal dosing in a BNF monograph? ## Questions people ask Q: Should I use eGFR or creatinine clearance for dosing? A: Use eGFR for most drugs. Use Cockcroft-Gault creatinine clearance for DOACs, narrow-therapeutic-index and nephrotoxic drugs, older patients and extremes of body weight, as the BNF advises. Q: At what eGFR is metformin avoided? A: The BNF advises avoiding metformin if eGFR is below 30 and reviewing the dose if it is below 45. Stop it during acute kidney injury. Q: What are sick-day rules? A: Temporary pausing of drugs such as ACE inhibitors, ARBs, diuretics, metformin, NSAIDs, sulfonylureas and SGLT2 inhibitors during dehydrating illness, restarting after 24 to 48 hours of normal eating and drinking. Q: Why avoid morphine in renal failure? A: Its active metabolites accumulate and cause prolonged sedation and respiratory depression. Other opioids with less renal clearance are usually preferred. Q: Why does trimethoprim raise creatinine? A: It blocks tubular secretion of creatinine, so serum creatinine rises without a true fall in GFR. It can also raise potassium. ## Related notes - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ - PSA calculation skills: doses, rates and units: https://passthepsa.com/psa-revision/calculations/ Sources: BNF; BNF guidance on prescribing in renal impairment; NICE guidance on acute kidney injury and chronic kidney disease; MHRA Drug Safety Update. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Drug interactions for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/drug-interactions/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: To answer an interaction question, identify the mechanism first: enzyme induction or inhibition, reduced excretion, chelation, or an additive effect such as QT prolongation, serotonin toxicity, hyperkalaemia or sedation. Then choose the safest action: avoid the pair, pick an alternative, adjust the dose, separate the timing or monitor. The BNF interactions section grades severity. ## How do you approach an interaction question? Find the newly started or stopped drug first, because most interactions follow a recent change. Then name the mechanism and the likely outcome. - Pharmacokinetic: absorption (chelation), metabolism (CYP450 induction or inhibition), excretion (renal competition). - Pharmacodynamic: additive or opposing effects at the same target or in the same organ. - Inhibitors act within days; inducers take one to two weeks to reach full effect and wear off over weeks after stopping. - Prefer substitution of the interacting drug over dose adjustment when a safe alternative exists. In the BNF, each drug has an Interactions link, and the Appendix on interactions lists pairs by severity. Severe interactions are those to avoid or to manage with specialist advice. ## Which drugs induce or inhibit CYP450? Inducers lower the levels of other drugs and inhibitors raise them. The classic exam inducers are rifampicin, carbamazepine, phenytoin and St John's wort. The classic inhibitors are clarithromycin and erythromycin, ciprofloxacin, azole antifungals, ritonavir and grapefruit juice. - Inducers reduce the effect of warfarin, DOACs, the combined and progestogen-only pills, ciclosporin and many others. - Inhibitors increase levels of warfarin, statins, carbamazepine, theophylline, ciclosporin, tacrolimus and DOACs. - Ciprofloxacin increases theophylline levels through CYP1A2 inhibition. - St John's wort is available over the counter, so ask about herbal remedies. ## High-yield interaction pairs: effect and action Pair | Effect | What to do --- | --- | --- Warfarin with macrolides, quinolones, azoles, metronidazole | INR rises; bleeding | Avoid or monitor INR closely; miconazole oral gel also interacts Warfarin with rifampicin or carbamazepine | INR falls; clots | Increase monitoring; dose adjustment needed Simvastatin or atorvastatin with clarithromycin | Statin levels rise; myopathy and rhabdomyolysis | Simvastatin: do not combine; suspend it during the course or choose another antibiotic. Atorvastatin: suspend or limit the dose per the BNF Methotrexate with trimethoprim or co-trimoxazole | Marrow suppression | Avoid Methotrexate with NSAIDs | Reduced methotrexate excretion | Caution; monitor, especially with renal impairment ACE inhibitor or ARB with spironolactone, potassium or trimethoprim | Hyperkalaemia | Check potassium; avoid or monitor ACE inhibitor or ARB, diuretic and NSAID | Acute kidney injury | Avoid the combination SSRI with MAOI, linezolid, tramadol or triptans | Serotonin syndrome | MAOI contraindicated; avoid or use caution Macrolide, quinolone, citalopram or antipsychotic with each other | QT prolongation; torsades | Avoid combining; correct potassium and magnesium; ECG Opioid with benzodiazepine or gabapentinoid | Sedation and respiratory depression | Use lowest doses; warn; avoid where possible Omeprazole or esomeprazole with clopidogrel | Reduced activation of clopidogrel | Avoid; the BNF suggests other PPIs Enzyme inducer with contraceptive pill or implant | Contraceptive failure | Use a non-affected method such as an IUD or injection Quinolone or tetracycline with calcium, iron or antacids | Chelation; poor absorption | Separate doses; check the BNF interval Nitrate with sildenafil | Severe hypotension | Contraindicated Azathioprine with allopurinol | Severe myelosuppression | Major azathioprine dose reduction, with specialist advice ## Which combinations cause hyperkalaemia, QT prolongation or serotonin syndrome? Hyperkalaemia combinations stack potassium-retaining drugs. ACE inhibitors, ARBs, spironolactone, eplerenone, trimethoprim, NSAIDs, heparin, ciclosporin and potassium supplements all raise potassium, and renal impairment multiplies the effect. QT prolongation is additive and worsened by low potassium and magnesium. Macrolides, quinolones, antipsychotics, citalopram, escitalopram, ondansetron, amiodarone, sotalol and methadone are common culprits. Diuretics add risk through hypokalaemia. Serotonin syndrome causes agitation, tremor, clonus, hyperthermia and diarrhoea. It follows combining serotonergic drugs, such as an SSRI with tramadol, linezolid, St John's wort or an MAOI. A washout period is required between an MAOI and an SSRI. ## What about sedation, contraception and absorption interactions? Opioids, benzodiazepines, gabapentinoids, sedating antihistamines and alcohol add central nervous system and respiratory depression, which is a recognised cause of death. Enzyme inducers reduce contraceptive pill and implant efficacy, so the pill is not reliable and a method such as the copper IUD or an injection is preferred. Absorption chelation is solved by timing: separate the cations from quinolones, tetracyclines, levothyroxine and bisphosphonates. Pharmacodynamic opposition also matters. Beta-blockers with verapamil or diltiazem risk bradycardia and heart block, and NSAIDs oppose antihypertensive therapy. Note: Check actions: the BNF grades each interaction by severity and gives the advice. Confirm the advice for the specific drug pair in the BNF. ## Check yourself - Name four CYP450 inducers and what they do to warfarin. - Name four CYP450 inhibitors. - Which antibiotic is the classic trap with simvastatin? - Which antibiotic should not be combined with methotrexate? - What is the triple whammy? - Which two PPIs should be avoided with clopidogrel? - Which contraceptive methods are not affected by enzyme inducers? - Which drugs separate from calcium or iron by timing? ## Questions people ask Q: Which antibiotics interact with warfarin? A: Macrolides, quinolones, metronidazole and co-trimoxazole commonly raise the INR. Rifampicin lowers it. Monitor the INR whenever an antibiotic is started or stopped. Q: Why is clarithromycin avoided with simvastatin? A: Clarithromycin inhibits CYP3A4 and raises statin levels, increasing the risk of myopathy and rhabdomyolysis. Simvastatin is not combined with it (suspend the statin or choose another antibiotic), and atorvastatin is suspended or dose-limited per the BNF. Q: What is the triple whammy? A: An NSAID with an ACE inhibitor or ARB and a diuretic, which together greatly increase the risk of acute kidney injury. Q: Which PPIs interact with clopidogrel? A: Omeprazole and esomeprazole reduce clopidogrel activation, so the BNF advises avoiding them and choosing another PPI if one is needed. Q: Do enzyme inducers affect all contraceptives? A: They reduce the efficacy of the combined and progestogen-only pills and the implant. The copper IUD and levonorgestrel IUS are not affected by enzyme induction. ## Related notes - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - Adverse drug reactions for the PSA: https://passthepsa.com/psa-revision/adverse-drug-reactions/ - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ Sources: BNF interactions guidance; MHRA Drug Safety Update; Faculty of Sexual and Reproductive Healthcare guidance on drug interactions with hormonal contraception. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Adverse drug reactions for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/adverse-drug-reactions/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: An adverse drug reaction is harm caused by a medicine at normal doses. Type A reactions are dose-related and predictable; type B are idiosyncratic or immune-mediated. To find the culprit, match the timing of onset to recent starts and dose changes, check the known side-effect profile, then dechallenge. Suspected reactions can be reported through the MHRA Yellow Card scheme. ## What are type A and type B adverse drug reactions? Type A reactions are augmented pharmacological effects of the drug, and they are the common ones. Type B reactions are bizarre, not predicted from the pharmacology, and rarer but more often serious. - Type A: dose-related, predictable, common, low mortality (hypoglycaemia with insulin, bleeding with warfarin, sedation with opioids). - Type B: dose-independent, idiosyncratic or immune-mediated, unpredictable, higher mortality (anaphylaxis, Stevens-Johnson syndrome, DRESS). - Type C: long-term use. Type D: delayed effects. Type E: end of use, such as withdrawal. Type F: failure of therapy, often from an interaction. Timing helps classify the reaction. Anaphylaxis occurs within minutes to hours, DRESS typically 2 to 8 weeks after starting, and cutaneous reactions such as Stevens-Johnson syndrome in the first weeks. Effects of amiodarone can appear months after starting. ## Classic drug and adverse reaction pairs Drug | Reaction | Key point --- | --- | --- ACE inhibitor | Dry cough; angioedema; hyperkalaemia | Cough is bradykinin-mediated; switch to an ARB. Angioedema can occur at any time; stop Statin | Myopathy; rhabdomyolysis | Muscle pain; check CK; risk with interacting drugs Amiodarone | Thyroid, lung, liver, corneal, skin effects | Long half-life; effects persist after stopping Lithium | Tremor, vomiting, confusion, ataxia, seizures | Toxicity with dehydration, NSAIDs, ACE inhibitors, thiazides Metoclopramide | Acute dystonia, oculogyric crisis | Young adults and children; short-term use only Sulfonylureas | Hypoglycaemia | Risk in renal impairment and older people SGLT2 inhibitors | Ketoacidosis, genital infection, volume depletion | DKA can occur with near-normal glucose; Fournier gangrene is rare Flucloxacillin, co-amoxiclav | Cholestatic jaundice | Can start after the course has finished Fluoroquinolones | Tendon rupture, neuropsychiatric effects | Stop at first tendon pain; extra risk with corticosteroids Allopurinol, carbamazepine, lamotrigine | Severe skin reactions | Early rash needs urgent review; lamotrigine needs slow titration Abacavir | Hypersensitivity | HLA-B*5701 testing before starting Beta-blockers | Bradycardia, bronchospasm, masked hypoglycaemia | Caution in asthma and diabetes ## How do you decide which drug caused a reaction? Work back from the onset of the problem to the most recent change in treatment. A new drug or dose increase in the right time window is the leading suspect. 1. List all drugs with start dates, dose changes and recent interacting additions. 2. Check whether the reaction fits the known profile of each drug in the BNF. 3. Check the timing: immediate, within weeks or after months. 4. Consider other causes, such as infection, disease progression or dehydration. 5. Dechallenge: stop the suspected drug and see whether the reaction settles. 6. Rechallenge only when safe, and never after a severe reaction such as angioedema or a severe cutaneous reaction. In a drug-induced liver injury, stop the suspected drug and look at the pattern of ALT versus ALP. In drug reaction questions, an old stable drug is usually less likely than a recent start, unless an interaction or worsening renal function has raised its level. ## What is anticholinergic burden? Anticholinergic burden is the cumulative effect of several drugs with antimuscarinic activity, and it is a classic cause of confusion and falls in older people. Effects include dry mouth, constipation, urinary retention, blurred vision, tachycardia and delirium. Common contributors are oxybutynin, tricyclic antidepressants such as amitriptyline, chlorphenamine, procyclidine and some antipsychotics. Review and stop where possible, and avoid starting anticholinergics in older people with dementia. ## What is the Yellow Card scheme, and how does the BNF list frequency? The Yellow Card scheme is the MHRA system for reporting suspected adverse reactions, and healthcare professionals, patients and carers can all report. Report all suspected reactions for black-triangle medicines and vaccines, and serious suspected reactions for established medicines. Proof of causation is not needed. The BNF lists side-effects by frequency, with very common being 1 in 10 or more, common 1 in 100 to 1 in 10, uncommon 1 in 1000 to 1 in 100, rare 1 in 10 000 to 1 in 1000, very rare fewer than 1 in 10 000, and frequency not known. Note: Check lists: use the BNF Side-effects section of the monograph, and the MHRA Drug Safety Update for newer warnings. Confirm details in the current BNF. ## Check yourself - What distinguishes a type A from a type B reaction? - Which ACE inhibitor reaction is a reason to avoid the class altogether? - What are the early features of lithium toxicity? - Which drug causes acute dystonia in young people? - Why can SGLT2 inhibitors cause ketoacidosis with a normal glucose? - How does flucloxacillin liver injury differ in timing? - How do you decide which drug caused a new rash? - What can be reported on a Yellow Card? ## Questions people ask Q: What is the difference between type A and type B reactions? A: Type A reactions are predictable, dose-related and common. Type B reactions are unpredictable, not dose-related, and rarer but more severe. Q: Why do ACE inhibitors cause a cough? A: They reduce bradykinin breakdown, causing a dry cough. An ARB is the usual alternative for cough. After ACE inhibitor angioedema, avoid the class and use an ARB only with caution and specialist advice. Q: Who can submit a Yellow Card? A: Healthcare professionals, patients and carers can all report suspected adverse reactions to the MHRA. Certainty about causation is not required. Q: What is anticholinergic burden? A: The combined antimuscarinic effects of multiple drugs, causing confusion, constipation, retention and falls, particularly in older people. Q: How does the BNF describe side-effect frequency? A: As very common, common, uncommon, rare, very rare or frequency not known, with defined ranges from 1 in 10 or more down to fewer than 1 in 10 000. ## Related notes - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ Sources: BNF; MHRA Yellow Card scheme; MHRA Drug Safety Update; NICE guidance. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Antibiotic prescribing for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/antibiotics/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: Safe antibiotic prescribing for the PSA follows Start Smart then Focus: confirm an indication, check the allergy history, choose the first-line agent from the BNF or local guidance, document the duration, and review at 48 to 72 hours to stop, switch to oral, change or continue. Then check renal function, interactions and C. difficile risk. ## What does Start Smart then Focus mean for prescribers? Start Smart then Focus is the UK antimicrobial stewardship approach: start promptly with a justified choice, then review and refine. - Start smart: document the indication and the allergy status, take cultures where this does not delay treatment, and follow local guidelines or the BNF first-line table. - Give IV antibiotics immediately in suspected sepsis with high-risk features. Do not delay them for investigations. - Prescribe a stop or review date. An open-ended course is a prescribing error. - Focus: review at 48 to 72 hours with the clinical picture and microbiology. The options are stop, switch IV to oral, change to a narrower agent, or continue with a documented duration. - Oral is the default when the patient can swallow and absorb and is not severely unwell. IV to oral switch is a recurring exam theme. ## How do I handle a reported penicillin allergy? Ask what happened, when, and what treatment was needed, because many penicillin allergy labels are wrong. History | Likely meaning | Prescribing consequence --- | --- | --- Urticaria, angioedema, wheeze or collapse soon after a dose | True immediate allergy | Avoid penicillins; take cross-reactivity advice from the BNF Severe delayed reaction such as blistering or organ involvement | True severe allergy | Avoid penicillins; seek specialist advice Nausea, vomiting or diarrhoea | Intolerance or side effect | Not an allergy; record it as such Unclear or remote history | Uncertain | Follow local penicillin allergy pathway Cross-reactivity with cephalosporins and carbapenems is mainly a concern after immediate or severe reactions. The BNF sets out the advice. For penicillin-allergic patients, the BNF and local guidance list alternatives for each infection. ## What are common first-line antibiotics? Use these as orientation only and always check the BNF and local guidance, which vary by area and resistance patterns. Infection | Usual first-line option | Exam point --- | --- | --- Sore throat needing antibiotics | Phenoxymethylpenicillin | Check penicillin allergy Low-severity community-acquired pneumonia | Amoxicillin | Severity assessment decides route and combinations Uncomplicated lower UTI in non-pregnant women | Nitrofurantoin, or trimethoprim where resistance risk is low | Check eGFR and pregnancy Non-severe cellulitis | Flucloxacillin | Check allergy; MRSA risk changes the choice ## Which antibiotic interactions and hazards does the exam favour? Antibiotic | Key hazard or interaction | Consequence --- | --- | --- Clarithromycin, erythromycin | Simvastatin, atorvastatin | Raised statin levels, myopathy; simvastatin: do not combine, atorvastatin: suspend or limit the dose (BNF) Clarithromycin | Warfarin | Raised INR; monitor closely Macrolides, quinolones | Other QT-prolonging drugs | QT prolongation, arrhythmia Rifampicin | Warfarin, DOACs, hormonal contraceptives, ciclosporin | Enzyme induction lowers their effect Trimethoprim | Methotrexate | Additive folate antagonism, bone marrow suppression Trimethoprim | ACE inhibitors, spironolactone | Hyperkalaemia Ciprofloxacin | Tizanidine | Raised tizanidine levels; avoid Quinolones | Theophylline, NSAIDs, corticosteroids | Seizures; tendon damage with corticosteroids Metronidazole | Alcohol, warfarin | Avoid alcohol; raised INR Flucloxacillin | Prolonged use | Cholestatic jaundice, which can appear after stopping Quinolone use is restricted by the MHRA to when other antibiotics are unsuitable because of disabling and potentially long-lasting side effects, including tendon rupture. ## How are gentamicin and vancomycin monitored, and how is MRSA treated? Gentamicin and vancomycin are nephrotoxic, so they need renal function and drug-level monitoring. - Gentamicin: dose by weight according to local protocol, check creatinine, and take levels as the protocol states. It is ototoxic and nephrotoxic; take care with other nephrotoxic drugs and loop diuretics. - Vancomycin: take trough levels before a dose, monitor renal function, and infuse IV slowly because rapid infusion causes infusion reactions. Oral vancomycin is not absorbed and is used for C. difficile. - MRSA is resistant to flucloxacillin and most other beta-lactams. Follow local microbiology advice, which commonly uses vancomycin or teicoplanin IV for serious infection, with level monitoring. ## Which antibiotics carry the highest C. difficile risk? Broad-spectrum antibiotics carry the greatest risk of C. difficile infection, including cephalosporins, clindamycin, quinolones and co-amoxiclav. - Older age, hospital stay and acid suppression with PPIs add to the risk. - If suspected, send a stool sample and stop any antibiotic that is not essential. - Avoid antimotility drugs such as loperamide. - NICE guidance lists oral vancomycin or fidaxomicin as first-line treatment; metronidazole is no longer first choice. Check the BNF. ## How do renal impairment, pregnancy and age change antibiotic choice? Renal impairment changes the dose or the choice of renally cleared antibiotics, so check the BNF renal impairment section. - Renal: aminoglycosides, vancomycin and trimethoprim need caution or adjustment. Nitrofurantoin is less effective and more toxic when renal function is low. Trimethoprim can raise creatinine without a true fall in GFR. - Pregnancy: penicillins, cephalosporins and erythromycin are generally considered acceptable. Avoid tetracyclines, and avoid quinolones and aminoglycosides unless essential. Trimethoprim is a folate antagonist and needs caution in the first trimester; nitrofurantoin is avoided near term. - Children: dose by weight or age band in the BNF for Children. Tetracyclines are avoided in younger children, and quinolones are used only when clearly justified. Note: Confirm in the BNF: these notes give principles, not doses. Check the first-line agent, dose, duration and renal adjustment in the BNF and local antimicrobial guidance before prescribing. ## Check yourself - What are the four review options at 48 to 72 hours? - What history separates penicillin allergy from intolerance? - Which macrolide interaction with a statin is most important? - Why does rifampicin make hormonal contraception unreliable? - What must be monitored when giving gentamicin? - Which antibiotic classes carry the most C. difficile risk? - Which antibiotic should be avoided with methotrexate? - Which antibiotics are avoided in pregnancy? ## Questions people ask Q: What is Start Smart then Focus? A: It is the UK stewardship approach: start antibiotics promptly with a documented indication and justified choice, then review at 48 to 72 hours and stop, switch to oral, change or continue. Q: Is every penicillin allergy label a true allergy? A: No. Nausea or diarrhoea is intolerance. Immediate reactions such as urticaria, angioedema or anaphylaxis, and severe delayed reactions, count as true allergy and should be avoided. Q: Why do clarithromycin and statins matter? A: Clarithromycin raises levels of some statins, especially simvastatin, increasing the risk of myopathy. Simvastatin should not be combined with it, so suspend the statin or choose another antibiotic; for atorvastatin, suspend it or limit the dose as the BNF advises. Q: Which antibiotics most often cause C. difficile infection? A: Broad-spectrum agents such as cephalosporins, clindamycin, quinolones and co-amoxiclav carry the most risk, particularly in older hospital patients. ## Related notes - Drug interactions for the PSA: https://passthepsa.com/psa-revision/drug-interactions/ - Renal dosing for the PSA: https://passthepsa.com/psa-revision/renal-dosing/ - Adverse drug reactions for the PSA: https://passthepsa.com/psa-revision/adverse-drug-reactions/ - Drug monitoring for the PSA: https://passthepsa.com/psa-revision/drug-monitoring/ Sources: BNF; BNF for Children; NICE guidance on antimicrobial prescribing; MHRA Drug Safety Update on fluoroquinolones; Start Smart then Focus antimicrobial stewardship toolkit. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions). --- # Emergency prescribing for the PSA Source: PassthePSA, PSA revision notes URL: https://passthepsa.com/psa-revision/emergency-prescribing/ Updated: 2026-10-01 Topic: UK Prescribing Safety Assessment (PSA) revision Short answer: Emergency prescribing in the PSA mostly means a once-only prescription for a time-critical drug: adrenaline 500 micrograms IM (1 in 1000) for adult anaphylaxis, a benzodiazepine first line in status epilepticus, naloxone for opioid overdose, and oxygen written as a target saturation range of 94-98%, or 88-92% when hypercapnic failure is a risk. ## What goes in the once-only section of the chart? The once-only section is for a single dose to be given at a stated time, such as an emergency drug, a premedication or a loading dose. - Write the drug, dose in a unit, route and the date and time, and sign it. - Do not write an emergency drug as a regular prescription. A repeating prescription for adrenaline or naloxone is an error, and the exam instruction line tells you which section the marks are on. - As-required drugs have their own section and need a maximum dose or frequency. - In a real emergency, give the drug immediately and document afterwards. ## How is anaphylaxis treated? Adrenaline is the first-line drug in anaphylaxis, given intramuscularly and as early as possible. - Adult dose: adrenaline 500 micrograms IM, which is 0.5 mL of 1 in 1000 (1 mg/mL), into the anterolateral thigh. It can be repeated after about 5 minutes if there is no improvement. - Children are dosed by age band: use the BNF for Children or the Resuscitation Council UK chart. - Do not confuse 1 in 1000 IM with 1 in 10 000, which is a different preparation used IV by experienced staff in specific circumstances. - Give high-flow oxygen, and IV fluids for hypotension. Antihistamines and corticosteroids are not part of initial treatment. ## What are the first-line drugs in other emergencies? Emergency | First-line principle | Exam trap --- | --- | --- Acute severe asthma | Oxygen, nebulised salbutamol, ipratropium and a systemic corticosteroid; IV magnesium on senior advice | Do not delay steroids; check the BNF for doses Hypoglycaemia | Fast-acting oral carbohydrate if able to swallow; IV glucose or IM glucagon (1 mg) if not | Recheck glucose and give longer-acting carbohydrate; glucagon works poorly in starvation and liver disease Status epilepticus | IV lorazepam (4 mg in an adult); buccal midazolam or rectal diazepam if no IV access | A benzodiazepine comes first; phenytoin, levetiracetam or valproate are second line Acute coronary syndrome | Aspirin 300 mg loading dose, analgesia and treatment per local pathway | Give oxygen only if saturation is below 94% Acute pulmonary oedema | Sit upright, oxygen only if hypoxic, IV furosemide for fluid overload. Nitrates are not routine: use GTN only for ongoing ischaemia or severe hypertension, and avoid if hypotensive | Opioids and nitrates are not routine; follow NICE and local guidance Hyperkalaemia with ECG changes | IV calcium gluconate, then insulin with glucose and nebulised salbutamol | Calcium protects the heart but does not lower potassium; stop contributing drugs Opioid overdose | Naloxone, titrated to respiratory rate | Naloxone wears off sooner than many opioids, so monitor and repeat ## What are the first-hour principles for sepsis? In suspected sepsis, speed matters: high-risk patients need IV antibiotics and fluids within the first hour, and others follow the NICE risk-stratified timings. - The Sepsis Six: give oxygen, take blood cultures, give IV antibiotics, give IV fluids, measure lactate and monitor urine output. - NICE guidance advises a crystalloid bolus of 500 mL over less than 15 minutes in adults who are hypotensive or have a high lactate, with reassessment after each bolus. - Choose the antibiotic from the local sepsis guideline and the allergy history. Check the BNF. ## How is oxygen prescribed as a drug? Oxygen is a drug and should be prescribed with a target saturation range, not a fixed flow rate. Patient group | Target saturation | Note --- | --- | --- Most acutely ill patients | 94-98% | Do not give routinely if saturation is already in range At risk of hypercapnic respiratory failure, such as COPD | 88-92% | Use controlled oxygen, such as a 24% or 28% Venturi mask, until blood gases are known In cardiac arrest, anaphylaxis and major trauma, give high-flow oxygen initially. Titrate down to the target range once the patient stabilises. ## How are IV fluids prescribed? A fluid prescription names the fluid, the volume and the rate or duration. - Resuscitation: NICE guidance advises a 500 mL crystalloid bolus over less than 15 minutes, then reassessment. - Routine maintenance: roughly 25-30 mL/kg/day of water with about 1 mmol/kg/day each of sodium, potassium and chloride, and 50-100 g/day of glucose. - Check electrolytes before adding potassium, and reduce rates in heart failure and renal impairment. Note: Confirm in the BNF: doses and volumes here are stable teaching figures, not instructions. Confirm every dose, route and age band in the BNF and local guidance. ## Check yourself - What is the adult IM adrenaline dose in anaphylaxis, and what volume of 1 in 1000 is it? - What is first-line in status epilepticus? - Why must naloxone be monitored after the first dose? - What target saturation applies to a patient with COPD? - Which drug protects the heart in hyperkalaemia but does not lower potassium? - What loading dose of aspirin is given in ACS? - What are the Sepsis Six? - Which chart section is used for an emergency drug? ## Questions people ask Q: What is the adrenaline dose for adult anaphylaxis? A: 500 micrograms IM, which is 0.5 mL of 1 in 1000 (1 mg/mL), repeated after about 5 minutes if there is no improvement. Children are dosed by age band. Q: What target oxygen saturation should I prescribe? A: Aim for 94-98% in most acutely ill patients and 88-92% in those at risk of hypercapnic respiratory failure, such as people with COPD. Q: What is first-line for status epilepticus? A: A benzodiazepine, usually IV lorazepam. If there is no IV access, buccal midazolam or rectal diazepam is used. Second-line drugs follow if seizures continue. Q: Why can naloxone need repeating? A: Its effect is shorter than that of many opioids, so respiratory depression can return. Patients need monitoring and may need repeat doses or an infusion. ## Related notes - High-risk medicines for the PSA: https://passthepsa.com/psa-revision/high-risk-medicines/ - How to write a safe prescription: https://passthepsa.com/psa-revision/prescribing-safely/ - PSA calculation skills: doses, rates and units: https://passthepsa.com/psa-revision/calculations/ - Antibiotic prescribing for the PSA: https://passthepsa.com/psa-revision/antibiotics/ Sources: BNF; Resuscitation Council UK anaphylaxis guidance; British Thoracic Society oxygen guideline; NICE guidance on sepsis, intravenous fluids and epilepsies; UK Kidney Association hyperkalaemia guideline. Exam-revision notes, not patient-specific advice; the BNF is the authority. More: https://passthepsa.com/psa-revision/ (all notes), https://passthepsa.com/psa/ (exam guide), https://passthepsa.com/ (practice questions).