Drug interactions
Fosphenytoin + Topiramate
Severity: Moderate
Fosphenytoin 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, the active form of fosphenytoin, lowers topiramate concentrations considerably. Topiramate may also increase phenytoin levels in some patients. Loss of seizure control or phenytoin toxicity may result.
What this interaction means in plain words
Fosphenytoin 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.
Fosphenytoin belongs to Central Nervous System; Topiramate belongs to Central Nervous System.
Why it happens
Phenytoin induces hepatic enzymes that metabolize topiramate, and topiramate may inhibit CYP2C19, raising phenytoin in some patients.
What to do
Monitor seizure control and phenytoin concentrations when topiramate is started or stopped, and adjust the topiramate dose upward if needed.
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 Topiramate
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Topiramate?
MediHelp rates the interaction as moderate. Fosphenytoin 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, the active form of fosphenytoin, lowers topiramate concentrations considerably. Topiramate may also increase phenytoin levels in some patients. Loss of seizure control or phenytoin toxicity may result.
How serious is the interaction between Fosphenytoin 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: Monitor seizure control and phenytoin concentrations when topiramate is started or stopped, and adjust the topiramate dose upward if needed.
What other medicines interact with Topiramate?
MediHelp also lists interactions of Topiramate with, for example, Benzhydrocodone / acetaminophen, Buprenorphine long-acting, Buprenorphine subdermal implant. The full list is on the Topiramate page.
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