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Phenytoin and Voriconazole: Drug Interaction Guide

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

Interaction severity: Major — avoid combination

How Phenytoin interacts with Voriconazole

Phenytoin induces CYP2C19 and CYP3A4 metabolism of voriconazole (reducing antifungal levels), while voriconazole inhibits phenytoin metabolism (raising phenytoin levels).

What you should do

Increase voriconazole maintenance dose to 5 mg/kg every 12 hours and monitor phenytoin levels; consider alternative antifungal.

Key facts

Severity

Major — avoid combination

Mechanism

Phenytoin induces CYP2C19 and CYP3A4 metabolism of voriconazole (reducing antifungal levels), while voriconazole inhibit...

Action

Increase voriconazole maintenance dose to 5 mg/kg every 12 hours and monitor phenytoin levels; consider alternative anti...

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 Phenytoin and Voriconazole together?

No — this combination should generally be avoided. Increase voriconazole maintenance dose to 5 mg/kg every 12 hours and monitor phenytoin levels; consider alternative antifungal.

What is the severity of this interaction?

The interaction between Phenytoin and Voriconazole is classified as Major — avoid combination. Phenytoin induces CYP2C19 and CYP3A4 metabolism of voriconazole (reducing antifungal levels), while voriconazole inhibits phenytoin metabolism (raising phenytoin levels).

What should I do if I'm prescribed both?

Increase voriconazole maintenance dose to 5 mg/kg every 12 hours and monitor phenytoin levels; consider alternative antifungal. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

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