skip to main content

Warfarin and metronidazole — GPhC CRA MCQ

Instant feedback + full explanation. One question, done properly.

ModerateDrug InteractionsWarfarin and metronidazoleGPhC CRA

A 67-year-old woman taking warfarin has a prescription for metronidazole 400 mg three times daily for dental infection. Her INR was 2.6 two days ago and she has no bleeding. What is the most important interaction to flag?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Metronidazole can increase anticoagulant effect and bleeding risk with warfarin

Metronidazole inhibits warfarin metabolism and can raise INR, increasing bleeding risk. The prescriber or anticoagulation clinic should be contacted for INR monitoring and possible dose adjustment. The patient should be counselled to report bruising, bleeding, black stools or severe headache. This is a high-risk interaction because the medicine has a narrow therapeutic index.

Reference: BNF