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Rifampicin and warfarin — GPhC CRA MCQ

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HardDrug InteractionsRifampicin and warfarinGPhC CRA

A patient taking warfarin for venous thromboembolism starts rifampicin for tuberculosis. The TB clinic asks the community pharmacy to flag the key issue. What is the most important interaction to flag?

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Correct answer: D — Rifampicin may reduce warfarin effect through enzyme induction

Rifampicin is a potent enzyme inducer and can reduce warfarin anticoagulant effect, lowering INR. Close anticoagulation management is needed because both starting and stopping rifampicin can destabilise warfarin dosing. The interaction may be substantial. It is not a serotonin or nitrate-like interaction.

Reference: BNF