Drug interactions
Phenytoin + Primidone
Severity: Moderate
Phenytoin and Primidone: 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 increases conversion of primidone to phenobarbital, raising phenobarbital levels and sedation. Primidone, via phenobarbital, can alter phenytoin concentrations.
What this interaction means in plain words
Phenytoin and Primidone 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; Primidone belongs to Central Nervous System.
Why it happens
Phenytoin induces primidone metabolism to phenobarbital, which in turn alters phenytoin metabolism.
What to do
Monitor phenytoin and phenobarbital levels and watch for sedation or loss of seizure control, adjusting doses 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 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 Primidone
- Lorlatinib + Primidone Contraindicated
- Lurasidone + Primidone Contraindicated
- Primidone + Ranolazine Contraindicated
- Primidone + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
- Primidone + Voriconazole Contraindicated
- Abiraterone + Primidone Major
Frequently asked questions
Can I take Phenytoin with Primidone?
MediHelp rates the interaction as moderate. Phenytoin and Primidone 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 increases conversion of primidone to phenobarbital, raising phenobarbital levels and sedation. Primidone, via phenobarbital, can alter phenytoin concentrations.
How serious is the interaction between Phenytoin and Primidone?
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 and phenobarbital levels and watch for sedation or loss of seizure control, adjusting doses as needed.
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.
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