At a glance
What this section is really testing
- Matching a new symptom, a new result or a new risk to the prescription that best explains it, using timing as the main clue.
- Recognising interactions on a list: the pair that together cause the problem, or the newly started drug that raised the level of an old one.
- Spotting the contraindicated prescription: a drug that should not be there given the patient's disease, allergy or organ function.
- Reading a chart under time pressure without checking every monograph, because the story tells you where to look.
A repeatable approach
- Read the problem firstBefore the chart: what has gone wrong, and when did it start?
- Find what changedA drug started or increased just before the problem is the prime suspect. Dates on the chart matter.
- Ask the timing questionDoes the interval fit? A rash on day 8 of a penicillin fits; a rash two years into amlodipine does not.
- Check the pairIf two drugs could act together, open one monograph's interactions and look for the other.
- Confirm, then tickOne lookup to confirm the mechanism. Then tick the prescription, not the drug that treats the problem.
Practise prescription review 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.
Scanning a chart without reading every monograph
Six drugs make fifteen possible pairs, and two minutes will not cover them. Read the chart with six questions, in this order, and stop as soon as one lights up.
A drug started this week. A drug whose level rises with a new macrolide or azole. An NSAID beside an ACE inhibitor and a diuretic. Anything newly added to warfarin. Check those pairs first.
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.
- Interactions that raise drug levels: macrolides, azoles, amiodarone, grapefruit
- Serotonin syndrome and other additive toxicities
- Bleeding risk: anticoagulants with antiplatelets and NSAIDs
- Hyperkalaemia and hyponatraemia from drug combinations
- Nephrotoxic combinations and dosing in renal impairment
- Anticholinergic burden in older patients
- QT prolongation
- Hypoglycaemia in treated diabetes
- Falls, sedation and postural hypotension
- Allergy and cross-reactivity
A real prescription review 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.
An 84-year-old woman is brought to the frailty assessment unit by her daughter, who says her mother has been muddled for about 2 weeks — losing the thread of conversations, drowsy in the afternoons, and constantly sipping water because her mouth is dry. She has opened her bowels twice in the past week, passing hard stools despite her usual laxative. Three weeks ago her general practitioner started a tablet for nausea, which has settled. Her bladder symptoms of urgency have been treated with the same tablet for 4 years. Her current prescriptions are shown.
PMH: Urge urinary incontinence; hypertension; hypercholesterolaemia; hypothyroidism; chronic constipation; osteoarthritis of the knees.
DH: As charted; no over-the-counter or herbal preparations; no known drug allergies.
SH: Lives alone with daily family visits; lifelong non-smoker; no alcohol.
On examination: Temperature 36.9°C, HR 96/min regular, BP 142/84 mmHg, RR 16/min, O2 sat 96% breathing air. Drowsy but rousable; inattentive, with an abbreviated mental test score of 6/10 against 9/10 documented at a clinic visit 4 months ago. Oral mucosa dry. Abdomen soft with palpable stool in the left iliac fossa; the bladder is palpable above the pubis after she has passed urine. No focal neurology.
Investigations: Na 139 mmol/L (133–146) K 4.2 mmol/L (3.5–5.3) Urea 6.0 mmol/L (2.5–7.8) Cr 74 µmol/L (45–90) eGFR 69 mL/min/1.73 m² (>60) Glucose 5.4 mmol/L (4.0–7.8) TSH 2.1 mU/L (0.3–4.2) CRP 4 mg/L (<5) Urine dipstick: negative for nitrites, leucocytes and blood
- amlodipine
- atorvastatin
- cyclizine
- levothyroxine
- paracetamol
- senna
- tolterodine
Answer and marking
cyclizine
Marks2
Explanation2 marks for ticking the cyclizine and nothing else. Assemble the picture first: two weeks of fluctuating confusion and drowsiness, a dry mouth she waters all day, hard infrequent stools, a resting rate of 96/min and a bladder still palpable after voiding — the peripheral and central signature of antimuscarinic excess. Then read the chart against time. The only prescription started inside the window is cyclizine, added 3 weeks ago for nausea. Its Summary of Product Characteristics (ADVANZ Pharma, revised February 2024) treats it 'as with other anticholinergic agents', warning of precipitated glaucoma and urinary retention, and lists 'Dryness of the mouth, nose and throat', 'Urinary retention' and disorientation among its effects — in a first-generation antihistamine this is expected pharmacology, and in an 84-year-old already on a bladder antimuscarinic it is predictable harm. The infective and metabolic mimics are all closed on paper: apyrexial, CRP 4, glucose, sodium and renal function normal, dipstick negative, TSH 2.1. The habit to take away: every new drug in a confused elderly patient is guilty until proved otherwise, and sedating antihistamines head the list.
tolterodine
Marks2
Explanation2 marks for ticking the tolterodine and nothing else. Anticholinergic burden is cumulative, and the question asks for the drug that set the baseline. Tolterodine is a bladder antimuscarinic: dry mouth is its commonest effect (35% against 10% with placebo in its SmPC), and confusion, hallucinations, disorientation and memory impairment are all reported reactions. Its Summary of Product Characteristics (Detrusitol, Viatris, revised January 2026) states the additive rule in terms: 'Concomitant medication with other drugs that possess antimuscarinic properties may result in more pronounced therapeutic effect and side-effects.' Four years of trouble-free use does not acquit it — it means she was compensating until a second antimuscarinic arrived. No other row competes: amlodipine, atorvastatin, paracetamol and senna have no antimuscarinic pharmacology in their SmPCs, and levothyroxine is closed by the in-range TSH. The management follows from the two ticks: stop the cyclizine, and review whether the tolterodine is still earning its place — in the frail elderly it usually is not.
Try another prescription review question →
More free prescription review questions, each with its full explanation
Before you submit
- Have I found the drug that fits the timing, not just one that could cause the problem?
- Did I tick the cause, not the treatment?
- Does the question want one prescription or two?
- If it is an interaction, have I named both halves?
- Have I checked organ function against the dose?
Practice questions
93 Prescription Review questions, easy to hard, marked like the exam
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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.