Metronidazole and Phenytoin: Drug Interaction Guide

Quick answer: This combination requires caution. Metronidazole and Phenytoin can be used together with adjustments and monitoring.

Interaction severity: Moderate — caution required

How Metronidazole interacts with Phenytoin

Metronidazole inhibits CYP2C9, reducing phenytoin metabolism and producing supratherapeutic levels with ataxia, nystagmus, and confusion.

What you should do

Monitor phenytoin levels during metronidazole therapy; reduce phenytoin dose if total or free levels rise.

Key facts

Severity

Moderate — caution required

Mechanism

Metronidazole inhibits CYP2C9, reducing phenytoin metabolism and producing supratherapeutic levels with ataxia, nystagmu...

Action

Monitor phenytoin levels during metronidazole therapy; reduce phenytoin dose if total or free levels rise.

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 Metronidazole and Phenytoin together?

With caution. Monitor phenytoin levels during metronidazole therapy; reduce phenytoin dose if total or free levels rise.

What is the severity of this interaction?

The interaction between Metronidazole and Phenytoin is classified as Moderate — caution required. Metronidazole inhibits CYP2C9, reducing phenytoin metabolism and producing supratherapeutic levels with ataxia, nystagmus, and confusion.

What should I do if I'm prescribed both?

Monitor phenytoin levels during metronidazole therapy; reduce phenytoin dose if total or free levels rise. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

Last reviewed: by iMedic Medical Editorial Team. Our editorial process.