Drug interactions
Folic acid + Phenytoin
Severity: Moderate
Folic acid and Phenytoin: 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, especially at high doses, can lower serum phenytoin levels and has been linked with reduced seizure control. Phenytoin can also lower folate levels, so supplementation is often needed.
What this interaction means in plain words
Folic acid and Phenytoin 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; Phenytoin belongs to Central Nervous System.
Why it happens
Folate may increase the hepatic metabolism of phenytoin, while phenytoin impairs folate absorption and status.
What to do
Monitor phenytoin levels and seizure frequency when starting or adjusting folic acid. Adjust the phenytoin dose if levels fall.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Folic acid and Phenytoin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 14 days on the web. No card needed.
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 Folic acid
- Ethotoin + Folic acid Moderate
- Folic acid + Fosphenytoin Moderate
- Folic acid + Glucarpidase Moderate
- Folic acid + Methotrexate Moderate
- Folic acid + Pafolacianine Moderate
- Folic acid + Phenobarbital Moderate
Frequently asked questions
Can I take Folic acid with Phenytoin?
MediHelp rates the interaction as moderate. Folic acid and Phenytoin 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, especially at high doses, can lower serum phenytoin levels and has been linked with reduced seizure control. Phenytoin can also lower folate levels, so supplementation is often needed.
How serious is the interaction between Folic acid and Phenytoin?
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 starting or adjusting folic acid. Adjust the phenytoin dose if levels fall.
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.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
