Drug interactions
Phenytoin + Topiramate
Severity: Moderate
Phenytoin and Topiramate: 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 lowers topiramate concentrations considerably. Topiramate may modestly raise phenytoin levels in some patients, which can cause toxicity.
What this interaction means in plain words
Phenytoin and Topiramate 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; Topiramate belongs to Central Nervous System.
Why it happens
Phenytoin induces topiramate metabolism, and topiramate may inhibit CYP2C19, which affects phenytoin clearance.
What to do
Titrate topiramate to clinical effect, as higher doses may be needed. Monitor phenytoin levels when topiramate is started or changed.
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 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
Other interactions of Topiramate
Frequently asked questions
Can I take Phenytoin with Topiramate?
MediHelp rates the interaction as moderate. Phenytoin and Topiramate 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 lowers topiramate concentrations considerably. Topiramate may modestly raise phenytoin levels in some patients, which can cause toxicity.
How serious is the interaction between Phenytoin and Topiramate?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Titrate topiramate to clinical effect, as higher doses may be needed. Monitor phenytoin levels when topiramate is started or changed.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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