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Warfarin and metronidazole — GPhC CRA MCQ

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HardDrug InteractionsWarfarin and metronidazoleGPhC CRA

A 70-year-old man taking warfarin for a metallic mitral valve is prescribed metronidazole 400mg three times daily for dental infection. His INR was 2.7 yesterday and he has a history of gastrointestinal bleeding. What is the most important interaction to flag?

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Correct answer: C — metronidazole can increase anticoagulant effect and bleeding risk

Metronidazole can potentiate warfarin and increase INR, raising bleeding risk. The risk is particularly important in a patient requiring anticoagulation for a mechanical valve and with previous bleeding. The pharmacist should contact the prescriber or anticoagulation clinic to agree an antibiotic plan and INR monitoring. The interaction does not reduce INR.

Reference: https://www.pharmacyregulation.org/students-and-trainees/pharmacist-education-and-training/registration-assessment