Ketoconazole and Warfarin: Drug Interaction Guide

Quick answer: This is a major interaction — avoid combining Ketoconazole and Warfarin unless specifically directed by your doctor.

How Ketoconazole interacts with Warfarin

Ketoconazole strongly inhibits CYP2C9 and CYP3A4, reducing metabolism of both warfarin enantiomers and significantly increasing INR and bleeding risk.

What you should do

Avoid combination if possible; otherwise reduce warfarin dose and monitor INR every 2-3 days at initiation.

Key facts

Severity

Major — avoid combination

Mechanism

Ketoconazole strongly inhibits CYP2C9 and CYP3A4, reducing metabolism of both warfarin enantiomers and significantly inc...

Action

Avoid combination if possible; otherwise reduce warfarin dose and monitor INR every 2-3 days at initiation.

Important medical disclaimer: This page provides educational information about drug interactions for general reference. It is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss your specific medications with a qualified healthcare provider before starting, stopping, or changing any treatment. About our editorial team.

Frequently asked questions

Can I take Ketoconazole and Warfarin together?

No — this combination should generally be avoided. Avoid combination if possible; otherwise reduce warfarin dose and monitor INR every 2-3 days at initiation.

What is the severity of this interaction?

The interaction between Ketoconazole and Warfarin is classified as Major — avoid combination. Ketoconazole strongly inhibits CYP2C9 and CYP3A4, reducing metabolism of both warfarin enantiomers and significantly increasing INR and bleeding risk.

What should I do if I'm prescribed both?

Avoid combination if possible; otherwise reduce warfarin dose and monitor INR every 2-3 days at initiation. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

Last reviewed: May 18, 2026 by iMedic Medical Editorial Team. Our editorial process.