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Fluconazole and Phenytoin: Drug Interaction Guide

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

Interaction severity: Moderate — caution required

How Fluconazole interacts with Phenytoin

Fluconazole inhibits CYP2C9 and CYP2C19, the principal enzymes metabolizing phenytoin, leading to elevated phenytoin levels with risk of nystagmus, ataxia, and confusion.

What you should do

Monitor phenytoin trough levels within 5-7 days of starting or stopping fluconazole and adjust dose to maintain free or total concentrations in therapeutic range.

Key facts

Severity

Moderate — caution required

Mechanism

Fluconazole inhibits CYP2C9 and CYP2C19, the principal enzymes metabolizing phenytoin, leading to elevated phenytoin lev...

Action

Monitor phenytoin trough levels within 5-7 days of starting or stopping fluconazole and adjust dose to maintain free or ...

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 Fluconazole and Phenytoin together?

With caution. Monitor phenytoin trough levels within 5-7 days of starting or stopping fluconazole and adjust dose to maintain free or total concentrations in therapeutic range.

What is the severity of this interaction?

The interaction between Fluconazole and Phenytoin is classified as Moderate — caution required. Fluconazole inhibits CYP2C9 and CYP2C19, the principal enzymes metabolizing phenytoin, leading to elevated phenytoin levels with risk of nystagmus, ataxia, and confusion.

What should I do if I'm prescribed both?

Monitor phenytoin trough levels within 5-7 days of starting or stopping fluconazole and adjust dose to maintain free or total concentrations in therapeutic range. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

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