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Pharmacology & Prescribing — UKMLA MCQ

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HardPharmacology & PrescribingUKMLAMRCGP AKTMRCP Part 1PSA

A patient taking lithium has new polyuria and is prescribed bendroflumethiazide for hypertension by an out-of-hours clinician. What is the safest action?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Avoid or urgently review; check lithium concentration and renal function

B is correct. Thiazide diuretics increase proximal tubular sodium and lithium reabsorption and can cause a clinically important rise in lithium concentration. The combination should generally be avoided or managed only with prescriber and specialist input, lithium-dose review and close concentration and renal monitoring. Polyuria also warrants assessment for nephrogenic diabetes insipidus and renal impairment. A concentration previously within the therapeutic range does not exclude later toxicity, particularly after an interacting medicine or dehydration. NSAIDs can further raise lithium concentrations. The patient should receive toxicity and sick-day advice and must not stop lithium abruptly without clinical direction.

Reference: NICE CG185, lithium interaction and monitoring recommendations: https://www.nice.org.uk/guidance/cg185/chapter/recommendations