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Rifampicin and warfarin — GPhC CRA MCQ

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HardDrug InteractionsRifampicin and warfarinGPhC CRA

A patient taking warfarin for a mechanical heart valve is started on rifampicin for tuberculosis. The anticoagulation clinic asks why INR has fallen. What is the most important interaction to flag?

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Correct answer: B — Rifampicin induces warfarin metabolism and can reduce anticoagulation

Rifampicin is a potent enzyme inducer and can reduce warfarin effect, lowering INR. Close anticoagulation monitoring and dose adjustment are required. The other options either delay appropriate care, use an unsuitable medicine, or miss the main safety issue.

Reference: BNF