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Warfarin and metronidazole — GPhC CRA MCQ

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HardDrug InteractionsWarfarin and metronidazoleGPhC CRA

A man taking warfarin is prescribed metronidazole 400mg three times daily for dental infection. His last INR was 2.6 and he has bruising on both arms. What is the most important interaction to flag?

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Correct answer: B — Metronidazole can increase INR and bleeding risk with warfarin

Metronidazole can potentiate warfarin and increase INR, raising bleeding risk. Existing bruising makes the interaction clinically important and warrants prescriber or anticoagulation clinic advice. INR monitoring and alternative antimicrobial consideration may be needed. The patient should be counselled to seek help for bleeding symptoms.

Reference: BNF