There is a warning in this months BNF.
•Miconazole, including the topical gel formulation, can enhance the anticoagulant effect of warfarin—if miconazole and warfarin are used concurrently, the anticoagulant effect should be carefully monitored and, if necessary, the dose of warfarin reduced
•Patients should be advised to tell their doctor or pharmacist if they are receiving warfarin before using products that contain miconazole (including those available without prescription), and to seek medical advice if they notice signs of over-anticoagulation during treatment, such as sudden unexplained bruising, nosebleeds or blood in the urine
Miconazole (Daktarin, Daktacort) is an antifungal indicated for prevention and treatment of various infections of the mouth, throat, skin, nails, or genitals. It is usually applied topically as a cream, ointment, powder, or oral gel. Some products are available without a prescription.
Warfarin is an oral anticoagulant that has been widely used since the 1950s for prophylaxis of thromboembolic events. Daily dose depends on individual requirements, and patients receiving long-term therapy require regular coagulation tests.
Drug interactions
The potential for drug interactions between miconazole and warfarin is well established1 2 3. The mechanism is understood to be inhibition by miconazole of one of the main cytochrome P450 isozymes involved in warfarin metabolism (CYP2C9), resulting in reduced warfarin clearance and an enhanced anticoagulant effect.
Prescribing information for products that contain miconazole warns that because miconazole inhibits CYP2C9, caution should be exercised for patients on oral anticoagulants such as warfarin, and the anticoagulant effect monitored (warfarin dose reduction may be needed). Patient Information Leaflets for miconazole products advise users to tell their doctor or pharmacist if they are taking warfarin.
