Drug interactions
Phenytoin + Rifapentine
Severity: Major
Phenytoin and Rifapentine: major 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
Rifapentine induces CYP2C9 and CYP3A4 and can lower phenytoin levels, risking loss of seizure control. Phenytoin may also reduce rifapentine exposure.
What this interaction means in plain words
Phenytoin and Rifapentine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Phenytoin belongs to Central Nervous System; Rifapentine belongs to Anti Bacterial.
Why it happens
Rifapentine induces CYP2C9/2C19 and CYP3A4, increasing phenytoin clearance.
What to do
Monitor phenytoin levels and seizure control, and raise the dose as needed. Re-evaluate the dose after rifapentine is stopped.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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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 Rifapentine
- Ledipasvir-sofosbuvir + Rifapentine Contraindicated
- Lorlatinib + Rifapentine Contraindicated
- Lurasidone + Rifapentine Contraindicated
- Ranolazine + Rifapentine Contraindicated
- Rifapentine + Sofosbuvir-velpatasvir Contraindicated
- Rifapentine + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Phenytoin with Rifapentine?
MediHelp rates the interaction as major. Phenytoin and Rifapentine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Rifapentine induces CYP2C9 and CYP3A4 and can lower phenytoin levels, risking loss of seizure control. Phenytoin may also reduce rifapentine exposure.
How serious is the interaction between Phenytoin and Rifapentine?
MediHelp rates it major, 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 control, and raise the dose as needed. Re-evaluate the dose after rifapentine is stopped.
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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