Fluconazole significantly increases warfarin blood levels, dramatically raising the risk of bleeding. This interaction can cause INR values to spike to dangerous levels, leading to spontaneous bleeding, including intracranial hemorrhage. Even a short course of fluconazole can have a prolonged effect on warfarin levels.
How This Interaction Works (Mechanism)
Fluconazole is a potent inhibitor of CYP2C9, the primary enzyme responsible for metabolizing the more potent S-enantiomer of warfarin. Inhibition of CYP2C9 reduces warfarin clearance, causing its plasma concentration to rise significantly. Fluconazole also inhibits CYP3A4, which metabolizes the less potent R-enantiomer. The combined effect can increase INR by 2 to 3 times the baseline value within 2 to 5 days.
Source: American Society of Health-System Pharmacists Drug Interaction Monograph, 2025
When fluconazole is necessary for a patient on warfarin, reduce the warfarin dose by 25 to 50 percent prophylactically. Check INR within 3 to 5 days of starting fluconazole and adjust the warfarin dose accordingly. Continue frequent INR monitoring throughout fluconazole treatment and for 1 to 2 weeks after stopping it, as the enzyme inhibition persists. Report any signs of bleeding immediately.
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Fluconazole and Warfarin have a severe interaction and should generally not be taken together without close medical supervision. The combination can cause serious, potentially life-threatening side effects. Contact your doctor immediately if you are currently taking both medications.
Fluconazole significantly increases warfarin blood levels, dramatically raising the risk of bleeding. This interaction can cause INR values to spike to dangerous levels, leading to spontaneous bleeding, including intracranial hemorrhage. Even a short course of fluconazole can have a prolonged effect on warfarin levels.
Yes. Anytime you are taking multiple medications, supplements, or substances, you should inform your doctor and pharmacist. They can evaluate your specific risk factors (age, kidney function, other medications, medical conditions) and determine whether the Fluconazole and Warfarin combination is safe for you, or whether adjustments are needed.
Related Resources
- Supplement interactions with Fluconazole on Health Britannica
- Supplement interactions with Warfarin on Health Britannica
- Fluconazole prices and pharmacy comparison on RxGrab
- Warfarin prices and pharmacy comparison on RxGrab
- Full drug interaction checker tool
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