Background: Fluconazole has been reported to interact with many medications. This study examined the effect of low-dose fluconazole therapy on the hypoprothrombinemic response of warfarin sodium in patients.
Methods: Patients receiving low-intensity anticoagulation therapy with warfarin were recruited. All patients were taking stable doses of warfarin and had two baseline prothrombin times (PTs) within 10% of each other. Each patient received 100 mg of fluconazole daily for 7 days. Prothrombin times were measured on days 2, 5, and 8 during fluconazole administration.
Results: All patients had a progressive increase in PTs. Mean (+/- SD) of PTs increased from 15.8 +/- 1 seconds before the administration of fluconazole to 18.9 +/- 1.9 seconds on day 5 and 21.9 +/- 2.2 seconds on day 8. Fluconazole therapy was stopped early in the three patients due to high PTs. The largest change in PT was 9.7 seconds. No bleeding was noted during the study.
Conclusion: Fluconazole predictably potentiates the hypoprothrombinemic response of warfarin. Prothrombin times must be monitored when fluconazole is administered to patients taking warfarin.