Hyperprothrombinemia as a result of a possible warfarin and intravaginal miconazole interaction.

Warfarin, a commonly prescribed anticoagulant, has many potential drug interactions. We describe a case of intravaginal miconazole potentiating the effects of warfarin in a patient previously stable on a consistent dose of 8.5 mg warfarin daily. Following a course of intravaginal miconazole and a dosage increase to 9 mg daily, her international normalized ratio (INR) increased from 2.0 to 5. After the course of miconazole was complete, the patient was stable with a therapeutic INR (mean INR 2.9) on 9 mg warfarin daily. Clinicians should consider the possibility of systemic absorption of intravaginal miconazole, and a resultant increase in warfarin's anticoagulant effect.