Attention has previously been drawn to the possibility of an interaction between miconazole oral gel (Daktarin Oral Gel®) and warfarin resulting in elevation of INR (1). The Australian Adverse Drug Reactions Advisory Committee (ADRAC) has now received 18 reports describing this interaction, which is the most serious and important of the reactions described in the 32 reports to ADRAC involving oral miconazole.
In most cases there was a clinically significant increase in the INR of patients who had been stabilized on warfarin. This usually occurred within a week or two of commencing miconazole. In the 17 patients in whom the INR values were documented, the INR rose to between 7.5 and more than 18. In 9 cases, there were no symptoms but in the other 8 cases, the patients presented with bruising, haematuria or mucocutaneous bleeding. Most patients required the withdrawal of one or both drugs. At least 9 patients were given vitamin K and 5 of these required fresh frozen plasma. Miconazole oral gel is absorbed to a sufficient extent to affect warfarin metabolism and hence increase its blood concentration and activity. This may occur through inflamed oral mucosa or from the bowel after swallowing the gel. An interaction is probably less likely when miconazole is administered to the skin or vaginally but ADRAC has received one report of an interaction involving topical miconazole cream.
Prescribers should be aware that the possibility of an interaction with warfarin is the most important adverse effect of oral miconazole. It is mentioned in the product information and the consumer medicine information for both oral and vaginal miconazole products. It should also be noted that miconazole products are available without prescription and pharmacists as well as doctors need to be alert to a possible interaction (2).
1. ADRAC. Interaction between miconazole oral gel and warfarin. Australian Adverse Drug Reactions Bulletin, 17: 7 (1998).
2. Australian Adverse Drug Reactions Bulletin, 21:4 (2002).