Metronidazole and Warfarin: Drug Interaction Guide
Quick answer: This is a major interaction — avoid combining Metronidazole and Warfarin unless specifically directed by your doctor.
How Metronidazole interacts with Warfarin
Metronidazole inhibits CYP2C9-mediated metabolism of the more potent S-enantiomer of warfarin, causing INR elevation and bleeding risk.
What you should do
Reduce warfarin dose by 25-50% at metronidazole initiation, check INR after 3-5 days and again after the antibiotic course ends.
Key facts
Severity
Major — avoid combination
Mechanism
Metronidazole inhibits CYP2C9-mediated metabolism of the more potent S-enantiomer of warfarin, causing INR elevation and...
Action
Reduce warfarin dose by 25-50% at metronidazole initiation, check INR after 3-5 days and again after the antibiotic cour...
Frequently asked questions
Can I take Metronidazole and Warfarin together?
No — this combination should generally be avoided. Reduce warfarin dose by 25-50% at metronidazole initiation, check INR after 3-5 days and again after the antibiotic course ends.
What is the severity of this interaction?
The interaction between Metronidazole and Warfarin is classified as Major — avoid combination. Metronidazole inhibits CYP2C9-mediated metabolism of the more potent S-enantiomer of warfarin, causing INR elevation and bleeding risk.
What should I do if I'm prescribed both?
Reduce warfarin dose by 25-50% at metronidazole initiation, check INR after 3-5 days and again after the antibiotic course ends. Always consult your prescribing clinician — do not stop or change medications without medical guidance.
Last reviewed: by iMedic Medical Editorial Team. Our editorial process.