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Warfarin antibiotic interaction — GPhC CRA MCQ

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ModerateCardiovascular TherapeuticsWarfarin antibiotic interactionGPhC CRA

A patient taking warfarin for a mechanical heart valve presents with a new prescription for metronidazole 400 mg three times daily. His last INR was 2.8 one week ago. He has no bleeding symptoms. What is the most important interaction to flag?

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Correct answer: D — Metronidazole may increase INR and bleeding risk

Metronidazole can increase the anticoagulant effect of warfarin and raise bleeding risk. The prescriber or anticoagulation clinic should be contacted so INR monitoring and dose advice can be arranged. The patient should also be counselled to report bruising, bleeding or black stools promptly.

Reference: BNF; NICE CKS