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Fluconazole-warfarin interaction — GPhC CRA MCQ

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ModerateDrug InteractionsFluconazole-warfarin interactionGPhC CRA

A patient taking warfarin for a mechanical valve presents a prescription for oral fluconazole. The current INR is stable and the next routine check is in four weeks. What should the pharmacist do?

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Correct answer: C — Query fluconazole and arrange an alternative or early INR-led management

Query fluconazole and arrange an alternative or early INR-led management: Fluconazole can increase warfarin effect and bleeding risk; the high-risk indication and distant routine INR check require a prospective plan rather than empirical patient-led dose changes. Supply fluconazole and retain the INR check scheduled in four weeks: A four-week delay is too long for an interaction that may raise INR during treatment. Supply fluconazole and halve warfarin on each antifungal treatment day: Warfarin dose changes must be individualised to INR and directed by the anticoagulation team. Pause warfarin for the entire fluconazole course and restart afterwards: Interrupting anticoagulation in a mechanical-valve patient creates serious thromboembolic risk. Supply fluconazole and add prophylactic low-dose oral vitamin K: Prophylactic vitamin K would destabilise anticoagulation and is not a substitute for interaction management.

Reference: BNF: warfarin sodium: https://bnf.nice.org.uk/drugs/warfarin-sodium/; BNF: fluconazole: https://bnf.nice.org.uk/drugs/fluconazole/