Drug interactions
Phenytoin + Pyrimethamine
Severity: Moderate
Phenytoin and Pyrimethamine: 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
Pyrimethamine is an antifolate and phenytoin can also lower folate status, so the combination may add to folate deficiency and megaloblastic changes. Phenytoin may also reduce pyrimethamine effect through enzyme induction, and seizure control is a concern.
What this interaction means in plain words
Phenytoin and Pyrimethamine 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; Pyrimethamine belongs to Anti Parasitic.
Why it happens
Additive antifolate effects, and possible induction of pyrimethamine metabolism by phenytoin.
What to do
Monitor blood counts and consider folinic acid supplementation during prolonged therapy. Watch for reduced antiparasitic response and for changes in phenytoin levels.
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 Pyrimethamine
- Deferiprone + Pyrimethamine Major
- Eliglustat + Pyrimethamine Major
- Acalabrutinib + Pyrimethamine Moderate
- Brexpiprazole + Pyrimethamine Moderate
- Dapsone + Pyrimethamine Moderate
- Folic acid + Pyrimethamine Moderate
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
Frequently asked questions
Can I take Phenytoin with Pyrimethamine?
MediHelp rates the interaction as moderate. Phenytoin and Pyrimethamine 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. Pyrimethamine is an antifolate and phenytoin can also lower folate status, so the combination may add to folate deficiency and megaloblastic changes. Phenytoin may also reduce pyrimethamine effect through enzyme induction, and seizure control is a concern.
How serious is the interaction between Phenytoin and Pyrimethamine?
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 blood counts and consider folinic acid supplementation during prolonged therapy. Watch for reduced antiparasitic response and for changes in phenytoin levels.
What other medicines interact with Pyrimethamine?
MediHelp also lists interactions of Pyrimethamine with, for example, Deferiprone, Eliglustat, Acalabrutinib. The full list is on the Pyrimethamine page.
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