Drug interactions
Fosphenytoin + Oxcarbazepine
Severity: Moderate
Fosphenytoin and Oxcarbazepine: 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
Oxcarbazepine, through its active metabolite, can raise phenytoin concentrations, especially at higher oxcarbazepine doses. Fosphenytoin is converted to phenytoin, so toxicity such as ataxia, nystagmus and sedation may develop.
What this interaction means in plain words
Fosphenytoin and Oxcarbazepine 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; Oxcarbazepine belongs to Central Nervous System.
Why it happens
The oxcarbazepine metabolite inhibits CYP2C19, reducing phenytoin metabolism.
What to do
Monitor phenytoin levels and signs of toxicity when starting or increasing oxcarbazepine. Reduce the phenytoin dose if concentrations rise.
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 Oxcarbazepine
- Cabotegravir + Oxcarbazepine Contraindicated
- Oxcarbazepine + Rilpivirine Contraindicated
- Artemether / lumefantrine + Oxcarbazepine Major
- Atazanavir + Oxcarbazepine Major
- Benzhydrocodone / acetaminophen + Oxcarbazepine Major
- Bictegravir + Oxcarbazepine Major
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 Oxcarbazepine?
MediHelp rates the interaction as moderate. Fosphenytoin and Oxcarbazepine 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. Oxcarbazepine, through its active metabolite, can raise phenytoin concentrations, especially at higher oxcarbazepine doses. Fosphenytoin is converted to phenytoin, so toxicity such as ataxia, nystagmus and sedation may develop.
How serious is the interaction between Fosphenytoin and Oxcarbazepine?
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 phenytoin levels and signs of toxicity when starting or increasing oxcarbazepine. Reduce the phenytoin dose if concentrations rise.
What other medicines interact with Oxcarbazepine?
MediHelp also lists interactions of Oxcarbazepine with, for example, Cabotegravir, Rilpivirine, Artemether / lumefantrine. The full list is on the Oxcarbazepine page.
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