Drug interactions
Phenytoin + Terbinafine
Severity: Moderate
Phenytoin and Terbinafine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin induces CYP3A4 and CYP2C9 and may lower terbinafine concentrations, potentially reducing antifungal efficacy. The magnitude is uncertain because terbinafine uses multiple pathways.
What this interaction means in plain words
Phenytoin and Terbinafine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Phenytoin belongs to Central Nervous System; Terbinafine belongs to Anti Fungals.
Why it happens
Phenytoin induces CYP3A4 and CYP2C9, increasing terbinafine metabolism.
What to do
Monitor antifungal response and consider a longer course or alternative agent if response is poor.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Terbinafine
- Terbinafine + Thioridazine Contraindicated
- Desipramine + Terbinafine Major
- Eliglustat + Terbinafine Major
- Flecainide + Terbinafine Major
- Imipramine + Terbinafine Major
- Maprotiline + Terbinafine Major
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Phenytoin with Terbinafine?
MediHelp rates the interaction as moderate. Phenytoin and Terbinafine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin induces CYP3A4 and CYP2C9 and may lower terbinafine concentrations, potentially reducing antifungal efficacy. The magnitude is uncertain because terbinafine uses multiple pathways.
How serious is the interaction between Phenytoin and Terbinafine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor antifungal response and consider a longer course or alternative agent if response is poor.
What other medicines interact with Terbinafine?
MediHelp also lists interactions of Terbinafine with, for example, Thioridazine, Desipramine, Eliglustat. The full list is on the Terbinafine page.
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