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Macrolide and warfarin — GPhC CRA MCQ

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ModerateDrug InteractionsMacrolide and warfarinGPhC CRA

A 69-year-old man on warfarin for a metallic heart valve is prescribed erythromycin for cellulitis. He asks whether he needs an extra INR test. What is the most important interaction to flag?

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

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Correct answer: D — Erythromycin may increase anticoagulant effect and bleeding risk

Macrolides such as erythromycin can increase warfarin effect and bleeding risk. A patient with a metallic valve is high risk if anticoagulation becomes unstable, so anticoagulation clinic involvement is important. The patient should be counselled on bleeding symptoms. Enzyme induction is not the usual concern with erythromycin.

Reference: BNF