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Warfarin and metronidazole — GPhC CRA MCQ

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HardDrug InteractionsWarfarin and metronidazoleGPhC CRA

A patient stabilised on warfarin is prescribed metronidazole 400 mg three times daily for dental infection. The dentist asks if supply is appropriate. What is the most important interaction to flag?

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Correct answer: A — Metronidazole can increase INR and bleeding risk

Metronidazole can potentiate warfarin and increase INR, causing bleeding risk. The anticoagulation clinic or prescriber should be involved and an alternative antimicrobial considered where appropriate. The other options either delay appropriate care, use an unsuitable medicine, or miss the main safety issue.

Reference: BNF