Warfarin Institute of America
Dedicated To Your Health
FLUCONAZOLE INTERACTION WITH WARFARIN
Brand Name: Diflucan
THIS INTERACTION IS VERY SUDDEN AND DRAMATIC. THE SERIOUSNESS OF THIS INTERACTION SHOULD NOT BE UNDERESTIMATED.
Mootha et al. report on the case of a 44-year-old man who was taking warfarin when he was prescribed fluconazole orally for a Candida infection in his eye. Unfortunately this report did not include the INR. However, the patient hemorrhaged into both eyes causing decreased visual acuity. The patient initially refused surgery on his eyes, but after two months when his vision was still declining, he reconsidered. His vision returned to 20/20 after surgery.
The accompanying comment with this case report states that the mechanism of action of this interaction is inhibition of the Cytochrome P45-2C9 enzyme in the liver. Since this enzyme is the principal metabolism route for warfarin, inhibition of it leads to an increased activity of warfarin.
Allison et al. reported a case of a spinal epidural hematoma as a result of the INR being raised due to the interaction of warfarin and fluconazole.
I have seen this interaction cause some very serious bruising. I have also seen the INR go from 2.8 to 6.9 in two days when fluconazole was added to the medications of someone taking warfarin. It appears than pharmacists filling orders for fluconazole when a patient is already on warfarin are prone to missing the warning about this interaction.
References:
Mootha VV et al. Intraocular hemorrhages due to warfarin fluconazole drug interaction in a patient with presumed Candida endophthalmitis. Arch Ophthalmol 2002;120:94-95
Allison EJ et al. Spinal epidural haematoma as a result of warfarin/fluconazole drug interaction. Eur J Emerg Med 2002;9:175-177
This reaction also happens with other members of this family: econazole, itraconazole, metronidazole, miconazole and voriconazole.
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Last updated November 7, 2004