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Warfarin and metronidazole — GPhC CRA MCQ

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HardCardiovascular TherapeuticsWarfarin and metronidazoleGPhC CRA

A woman taking warfarin for a mechanical heart valve presents a prescription for metronidazole 400 mg three times daily. Her INR was checked two weeks ago and was stable. What is the most important interaction to flag?

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

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Correct answer: C — Increased anticoagulant effect with a raised bleeding risk

Metronidazole can increase warfarin effect and may cause clinically significant INR elevation. The best answer addresses the key safety, legal or pharmaceutical care issue in the vignette. The other options would either delay appropriate care, create a new risk, or fail to resolve the issue. This is consistent with the cited UK reference for safe pharmacy practice.

Reference: BNF; NICE CKS