Miconazole Warfarin Interaction — MFDS Part 1 MCQ
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Correct answer: E — It inhibits CYP2C9, reducing S-warfarin metabolism and increasing the INR
Explanation lettering: E = shown as A · A = shown as E
A is correct. Miconazole is systemically absorbed from the oral gel and inhibits CYP2C9. S-warfarin, the more pharmacologically potent warfarin enantiomer, is metabolised mainly by CYP2C9. Inhibiting this pathway reduces warfarin clearance, potentially increasing its plasma concentration, INR and risk of serious bleeding. CYP2C9 induction would have the opposite effect, so B is incorrect. Miconazole does not produce this interaction by reducing warfarin absorption, suppressing platelet production or directly inhibiting factor Xa, excluding C, D and E. The combination therefore requires particular caution and careful anticoagulant monitoring where concomitant use is contemplated.
Reference: Electronic Medicines Compendium, Warfarin 0.5 mg Tablets, Summary of Product Characteristics, section 4.5 Interactions. https://www.medicines.org.uk/emc/product/15258/smpc