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Warfarin antibiotic interaction — GPhC CRA MCQ

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ModerateCardiovascular TherapeuticsWarfarin antibiotic interactionGPhC CRA

A patient stabilised on warfarin presents with a prescription for metronidazole from the dentist. Their INR was in range last week and they have no bleeding symptoms. 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: B — Increased INR and bleeding risk from metronidazole

Metronidazole can potentiate warfarin and increase INR and bleeding risk. The pharmacist should flag the interaction and arrange appropriate INR monitoring or prescriber review. In this scenario, the correct option is increased INR and bleeding risk from metronidazole. The other options are plausible but do not address the key clinical, legal or safety issue as directly. This aligns with UK pharmacy practice guidance cited in the reference field.

Reference: BNF; Stockley's Drug Interactions