Fluorouracil and Phenytoin: Drug Interaction Guide

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

Interaction severity: Moderate — caution required

How Fluorouracil interacts with Phenytoin

Fluorouracil can inhibit CYP2C9-mediated phenytoin metabolism, increasing phenytoin concentrations and neurotoxicity risk.

What you should do

Measure phenytoin concentrations and assess for nystagmus, ataxia, confusion, and sedation during and after fluorouracil therapy. Adjust phenytoin as needed.

Key facts

Severity

Moderate — caution required

Mechanism

Fluorouracil can inhibit CYP2C9-mediated phenytoin metabolism, increasing phenytoin concentrations and neurotoxicity ris...

Action

Measure phenytoin concentrations and assess for nystagmus, ataxia, confusion, and sedation during and after fluorouracil...

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 Fluorouracil and Phenytoin together?

With caution. Measure phenytoin concentrations and assess for nystagmus, ataxia, confusion, and sedation during and after fluorouracil therapy. Adjust phenytoin as needed.

What is the severity of this interaction?

The interaction between Fluorouracil and Phenytoin is classified as Moderate — caution required. Fluorouracil can inhibit CYP2C9-mediated phenytoin metabolism, increasing phenytoin concentrations and neurotoxicity risk.

What should I do if I'm prescribed both?

Measure phenytoin concentrations and assess for nystagmus, ataxia, confusion, and sedation during and after fluorouracil therapy. Adjust phenytoin as needed. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

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