Drug interactions
Phenytoin + Rifabutin
Severity: Moderate
Phenytoin and Rifabutin: 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 may lower rifabutin concentrations, risking reduced antimycobacterial efficacy and resistance. Rifabutin may also alter phenytoin levels, so seizure control can be affected in either direction.
What this interaction means in plain words
Phenytoin and Rifabutin 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; Rifabutin belongs to Anti Bacterial.
Why it happens
Phenytoin induces CYP3A4 to speed rifabutin metabolism, while rifabutin is itself an inducer that can lower phenytoin concentrations.
What to do
Monitor serum phenytoin concentrations and clinical response to both drugs, adjusting phenytoin dosing as needed. Consider rifabutin therapeutic drug monitoring or a higher dose if the infection responds poorly.
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 Rifabutin
- Cabotegravir + Rifabutin Contraindicated
- Lorlatinib + Rifabutin Contraindicated
- Rifabutin + Voriconazole Contraindicated
- Apixaban + Rifabutin Major
- Axitinib + Rifabutin Major
- Brexpiprazole + Rifabutin Major
Frequently asked questions
Can I take Phenytoin with Rifabutin?
MediHelp rates the interaction as moderate. Phenytoin and Rifabutin 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 may lower rifabutin concentrations, risking reduced antimycobacterial efficacy and resistance. Rifabutin may also alter phenytoin levels, so seizure control can be affected in either direction.
How serious is the interaction between Phenytoin and Rifabutin?
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 serum phenytoin concentrations and clinical response to both drugs, adjusting phenytoin dosing as needed. Consider rifabutin therapeutic drug monitoring or a higher dose if the infection responds poorly.
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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