Drug interactions
Folic acid + Fosphenytoin
Severity: Moderate
Folic acid and Fosphenytoin: 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
Folic acid supplementation can lower phenytoin concentrations, which are the active form of fosphenytoin, and may lead to loss of seizure control. The effect is more likely with higher folate doses.
What this interaction means in plain words
Folic acid and Fosphenytoin 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.
Folic acid belongs to Miscellaneous; Fosphenytoin belongs to Central Nervous System.
Why it happens
Folate may increase phenytoin metabolism; the exact mechanism is not firmly established.
What to do
Monitor phenytoin levels and seizure frequency when folic acid is started or changed. Adjust the fosphenytoin dose as 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 Folic acid
- Ethotoin + Folic acid Moderate
- Folic acid + Glucarpidase Moderate
- Folic acid + Methotrexate Moderate
- Folic acid + Pafolacianine Moderate
- Folic acid + Phenobarbital Moderate
- Folic acid + Phenytoin Moderate
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 Folic acid with Fosphenytoin?
MediHelp rates the interaction as moderate. Folic acid and Fosphenytoin 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. Folic acid supplementation can lower phenytoin concentrations, which are the active form of fosphenytoin, and may lead to loss of seizure control. The effect is more likely with higher folate doses.
How serious is the interaction between Folic acid and Fosphenytoin?
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 seizure frequency when folic acid is started or changed. Adjust the fosphenytoin dose as needed.
What other medicines interact with Folic acid?
MediHelp also lists interactions of Folic acid with, for example, Ethotoin, Glucarpidase, Methotrexate. The full list is on the Folic acid page.
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