OBJECTIVE: A retrospective case series published in 2012 concluded that 
miconazole and nystatin used as topical antifungal drugs appear to interact 
equally strongly with warfarin. If confirmed, this finding has significant 
implications for clinical practice. This study evaluates the evidence.
MATERIALS AND METHODS: Evidence from the pharmacology literature, the medical 
literature and the 'yellow card' adverse drug reaction surveillance reports was 
analysed regarding possible interactions of nystatin and miconazole with 
warfarin.
RESULTS: There is strong evidence to support the derangement of warfarin 
anticoagulation by miconazole oral gel in all areas of evidence studied. No 
postulated mechanism of interaction, no additional published reported cases and 
no supportive data from adverse drug reports were identified which would 
corroborate the case for a significant interaction between nystatin and 
warfarin.
CONCLUSION: Miconazole and nystatin used as topical antifungal drugs do not 
interact equally strongly with warfarin. Miconazole oral gel can clearly 
interact with warfarin to cause derangement of anticoagulation. Nystatin appears 
unlikely to interact with warfarin.