Yeast treatment may affect warfarin therapy

NEW YORK (Reuters Health) – For women taking warfarin to
prevent blood clots, a single dose of fluconazole to treat a
vaginal yeast infection can lead to an increased risk of
bleeding, findings from a small study suggest.

The time taken for blood to clot — the so-called
prothrombin time — should therefore be carefully monitored in
this scenario, and a change in warfarin dose may be needed, the
author advises.

Fluconazole (brand name, Diflucan) is a common treatment
for vaginal candidiasis, and is known to interact with a number
of drugs, including warfarin — which can give rise to serious
bleeding complications — according to the report in the
medical journal Obstetrics and Gynecology.

While a few studies have looked at the effect of several
days of fluconazole therapy on bleeding risk in warfarin users,
until now none had looked at the impact of a single dose.

The study involved six women who had been on warfarin
therapy for at least 6 months and had no dose changes in the
last 4 weeks. Prothrombin time and other blood-clotting
measurements were taken at the start of the study and then
repeated 2, 5, and 8 days after the participants took one
150-milligram dose of fluconazole.

Prothrombin times increased by 11 percent, 34 percent and 2
percent at each time point, respectively, Dr. Mark A.
Turrentine, from the Kelsey-Seybold Clinic in Houston, found.

Following the fluconazole dose, three of the women required
a decrease in warfarin dose.

Because the difference between a dangerous dose and an
effective dose of warfarin is so narrow, and given the
“individual sensitivity demonstrated by a portion of the
population, some alteration of the dose of warfarin may be
necessary when patients are given even a single dose of
fluconazole,” Turrentine concludes.

SOURCE: Obstetrics and Gynecology, February 2006.