Drug interactions
ketoconazole + warfarin
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Overview
Ketoconazole inhibits warfarin metabolism, increasing INR and bleeding risk.
Mechanism of action
Inhibition of CYP2C9 and CYP3A4 by ketoconazole → ↑ warfarin exposure → ↑ anticoagulant effect.
Clinical management
If used together, monitor INR more frequently when ketoconazole is started or stopped and adjust warfarin dose accordingly. Counsel on bleeding signs.
Drug reference
References
- Warfarin (Coumadin) Prescribing Information – Drug Interactions — FDA Label
- Warfarin: Drug interactions (azole antifungals) — Lexicomp
- Warfarin and azole antifungals — UpToDate
Frequently asked questions
Can I take ketoconazole with warfarin?
The interaction is rated: Major. Ketoconazole inhibits warfarin metabolism, increasing INR and bleeding risk.
How serious is the interaction between ketoconazole and warfarin?
The interaction is rated: Major. Evidence level: High.
How is the interaction between ketoconazole and warfarin managed?
If used together, monitor INR more frequently when ketoconazole is started or stopped and adjust warfarin dose accordingly. Counsel on bleeding signs.
Why do ketoconazole and warfarin interact?
Inhibition of CYP2C9 and CYP3A4 by ketoconazole → ↑ warfarin exposure → ↑ anticoagulant effect.
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