At a glance
What this section is really testing
- Recognising the clinical problem that needs a drug now, and which one. The case usually contains the indication in plain sight; the discrimination is between the credited drug and its near neighbours.
- Writing the prescription as a prescription, not as a drug name: a dose in the right unit, a route the drug can actually be given by, a frequency, and where the scheme states one, a duration.
- Applying the patient to the dose: weight, age, renal function, pregnancy, and the interaction that changes the usual choice.
- Using the chart correctly. Once-only, regular and as-required sections are different forms, and the instruction line tells you which one the marks are on.
A repeatable approach
- Name the indicationSay in one phrase what the drug is for. If you cannot, you are not ready to choose one.
- Choose the class, then the drugThe BNF treatment summary gives the class and first-line agent; the case's modifiers pick the drug within it.
- Find the dose under the right indicationMonographs list several indications with different doses. Read the heading, not the first number.
- Apply the patientWeight-based? Renal impairment? Age band? Pregnancy? Each can change the dose or the drug.
- Write it as the chart needs itDose in a unit, route from the accepted list, frequency in words the chart uses, once-only or regular as instructed.
Practise prescribing questions →
BNF strategy for this section
The exam is open book, and the time is short. Know which heading answers which question before you open the monograph.
The general technique, with drills, is in the BNF speed guide.
The anatomy of a credited prescription
Every prescribing item is marked in two halves, and the halves are independent. You can score full marks for the drug and nothing for the prescription, or the reverse.
Five marks for the drug group, five for medicine, dose, route and frequency together. Some schemes credit a lower tier: right drug and route but a dose written as a volume, for example, keeps the drug marks and loses one prescription mark. The worked example below shows a real scheme.
The final prescription check
- Correct patient: weight, age, pregnancy, allergy
- Correct medicine, generic, for this indication
- Correct dose from the matching indication, in a unit
- Correct route for this form
- Correct frequency, and duration if the scheme wants one
- Renal or hepatic adjustment applied
- Contra-indications and allergy checked
- Interactions with the chart checked
Common traps
Areas worth being comfortable with
Not predictions. These are the broad clinical areas this section draws on, taken from the shape of the exam and the BNF; being fluent in them makes the lookup fast.
- Analgesia, including the WHO ladder and opioid conversion
- Antibiotics for common community and hospital infections
- Anticoagulation: initiation, reversal and bridging
- Fluids and electrolyte replacement
- Diabetes: insulin regimens and hypoglycaemia
- Asthma and COPD acute treatment
- Anaphylaxis and other emergency once-only drugs
- Nausea, constipation and other symptom control
- Steroids: dosing and sick-day rules
- Thromboprophylaxis
A real prescribing question from the bank
This is one of the 20 items every visitor can try free, in the interface the exam uses. Work it before you open the answer.
A 58-year-old man is admitted to the acute medical unit with community-acquired pneumonia. He is breathless walking to the bathroom and is expected to spend most of the next few days in bed. The admission venous thromboembolism risk assessment scores him at increased risk of thrombosis and low risk of bleeding, and the consultant asks for pharmacological thromboprophylaxis to be prescribed alongside the antibiotic. He has never had a thrombosis and has never taken an anticoagulant.
PMH: Type 2 diabetes mellitus; hypertension.
DH: metformin 500 mg PO twice daily (12-hrly); amlodipine 5 mg PO daily; doxycycline 100 mg PO daily (started today for the pneumonia). No known drug allergies.
SH: non-smoker; drinks 8 units of alcohol a week; delivery driver.
On examination: Temperature 38.1°C, HR 96/min and regular, BP 128/76 mmHg, RR 22/min, O2 sat 94% breathing air. Weight 82 kg. Right basal crackles with dullness to percussion. No calf swelling or tenderness. No rash, no bruising, no bleeding.
Investigations: Na 136 mmol/L (135–145) K 4.2 mmol/L (3.5–5.3) Urea 6.2 mmol/L (2.5–7.8) Creatinine 76 µmol/L (60–120) Hb 148 g/L (130–180) WCC 13.6 ×10⁹/L (4.0–11.0) Platelets 322 ×10⁹/L (150–400) CRP 118 mg/L (<5) Chest X-ray: right lower lobe consolidation
Answer and marking
enoxaparin sodium 40 mg/0.4 mL pre-filled syringe (Clexane®) · 40 mg · subcutaneous (SC) · once daily
Marks5 for the drug choice, 5 for the written prescription (dose, route, frequency).
Also creditedenoxaparin; enoxaparin sodium; Clexane; Inhixa; dalteparin; dalteparin sodium; Fragmin
Drug choiceAn acutely ill medical inpatient whose mobility has just collapsed is exactly who pharmacological thromboprophylaxis is for, and the risk assessment printed with the case has already made the decision to treat — increased thrombosis risk, low bleeding risk. The UK answer is a low molecular weight heparin, and the BNF doses two of them for this precise indication: enoxaparin 40 mg every 24 hours, dalteparin 5000 units every 24 hours, both subcutaneous. Either earns full marks. Fondaparinux 2.5 mg once daily is a licensed, NICE-listed alternative and loses one mark on drug choice only. Tinzaparin is the trap inside the class: its prophylaxis licences are surgical (3500 units general surgery, 4500 units orthopaedic) and it has no medical-patient dose to write. Unfractionated heparin 5000 units twice daily is kept for patients who cannot have a low molecular weight heparin — severe renal impairment, mainly — and this man's creatinine clearance is about 109 mL/minute. The direct oral anticoagulants fail on licence: rivaroxaban and apixaban cover prophylaxis only after hip or knee replacement, and trials of extended oral prophylaxis in medical patients bought extra bleeding for no net benefit. Aspirin is an antiplatelet, and NICE NG89 says in terms not to use it for this purpose.
Dose, route and frequencyThe dose is 40 mg — or, as the Clexane SmPC itself writes it, 4,000 IU — subcutaneously once daily. The number that catches people is 20. Twenty milligrams is a real enoxaparin dose twice over: the moderate-risk surgical dose, and the prophylaxis dose when creatinine clearance falls to 15–30 mL/minute. Neither applies to a 58-year-old with a creatinine of 76 µmol/L, and half-dose prophylaxis in normal renal function is under-protection. In the other direction, 1 mg/kg twice daily and 1.5 mg/kg once daily are TREATMENT doses — for a thrombosis he does not have — and score nothing for the prescription half, as does 40 mg written twice daily, which is the same 80 mg a day by another route. Check the platelet count before starting any heparin (his is 322 ×10⁹/L, printed) and remember the count needs rechecking if he is still on it after 4 days.
Credited answersenoxaparin sodium 40 mg/0.4 mL pre-filled syringe (Clexane®/Inhixa®) — 40 mg (4,000 units), subcutaneous (SC), once daily. Full marks. dalteparin sodium 5000 units/0.2 mL (Fragmin®) — 5000 units, subcutaneous (SC), once daily. Full marks. Also credited for drug choice: fondaparinux 2.5 mg SC once daily (4 + 5); unfractionated heparin 5000 units SC twice daily (2 + 5); tinzaparin (3 + 0); 'low molecular weight heparin' unnamed (2 + 0). rivaroxaban, apixaban, warfarin, aspirin — 0/10. (BNF, enoxaparin sodium and dalteparin sodium monographs, and Clexane SmPC, all read 22 August 2026.)
How this item is marked
Every answer is matched to a marking tier. The first rows below are from this item's real scheme (33 tiers in total).
| Medicine | Dose and route | Marks | Marking note |
|---|---|---|---|
| enoxaparin | 40 mg · subcutaneous (SC) | 10 / 10 | optimal. BNF, prophylaxis of deep-vein thrombosis in medical patients: 'By subcutaneous injection, Adult: 40 mg every 24 hours.' Normal renal function (Cockcrof… |
| enoxaparin | 4000 units · subcutaneous (SC) | 10 / 10 | the same dose written in units — the Clexane SmPC's own spelling is '4,000 IU (40 mg) once daily'. The scorer compares mass and unit doses separately, so the un… |
| Clexane | 40 mg · subcutaneous (SC) | 10 / 10 | the same prescription under the brand name; biological medicines are in any case prescribed by brand. Credited identically. |
| Inhixa | 40 mg · subcutaneous (SC) | 10 / 10 | the biosimilar brand. Credited identically. |
| dalteparin | 5000 units · subcutaneous (SC) | 10 / 10 | the co-equal alternative: BNF, prophylaxis of deep-vein thrombosis in medical patients, 'By subcutaneous injection, Adult: 5000 units every 24 hours.' Any UK tr… |
| Fragmin | 5000 units · subcutaneous (SC) | 10 / 10 | dalteparin under its brand name. Credited identically. |
| enoxaparin | 20 mg · subcutaneous (SC) | 6 / 10 | the renal-impairment dose (creatinine clearance 15–30 mL/minute) or the moderate-risk surgical dose, given to a man whose creatinine clearance is about 109 mL/m… |
| enoxaparin | 2000 units · subcutaneous (SC) | 6 / 10 | the same under-dose written in units (2,000 IU = 20 mg). Deduct 4. |
Try another prescribing question →
More free prescribing questions, each with its full explanation
Before you submit
- Is the drug I chose the first-line agent for this indication, in this patient?
- Is the dose taken from the right indication in the monograph?
- Have I written a dose in a unit, not a volume?
- Does the route exist for this drug and this form?
- Is there a frequency, and is it in the chart's words?
- Have I checked renal function, allergy and the interaction the case mentions?
Practice questions
92 Prescribing questions, easy to hard, marked like the exam
Every answer comes with the explanation and the BNF reference behind it. Twenty questions across all eight sections are free. Pass guarantee: fail after 400+ questions and your access is extended free for 3 months.
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Section weightings follow the published PSA blueprint. The BNF headings named here are the current online BNF's. Check any dose or threshold against the BNF before you rely on it; this page teaches the method, the BNF holds the numbers.