Drug interactions
Phenytoin + Prednisone
Severity: Moderate
Phenytoin and Prednisone: moderate interaction.
Last updated Sources: US FDA label
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 is a strong inducer of CYP3A4 and can substantially increase the clearance of prednisolone, reducing corticosteroid effect. Prednisone may also alter phenytoin levels unpredictably.
What this interaction means in plain words
Phenytoin and Prednisone 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; Prednisone belongs to Endocrine.
Why it happens
Phenytoin induction of CYP3A4 and P-glycoprotein increases corticosteroid clearance.
What to do
Monitor clinical response and increase the prednisone dose as needed; check phenytoin concentrations when starting or stopping prednisone.
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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References
- Prednisone - FDA drug label (DailyMed) — openFDA / DailyMed
Other interactions of Prednisone
- Bcg vaccine live + Prednisone Contraindicated
- Measles vaccine + Prednisone Contraindicated
- Mifepristone + Prednisone Contraindicated
- Prednisone + Radium-223 dichloride Contraindicated
- Prednisone + Smallpox vaccine live Contraindicated
- Adenovirus types 4 and 7 live + Prednisone Major
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 Prednisone?
MediHelp rates the interaction as moderate. Phenytoin and Prednisone 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 is a strong inducer of CYP3A4 and can substantially increase the clearance of prednisolone, reducing corticosteroid effect. Prednisone may also alter phenytoin levels unpredictably.
How serious is the interaction between Phenytoin and Prednisone?
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 clinical response and increase the prednisone dose as needed; check phenytoin concentrations when starting or stopping prednisone.
What other medicines interact with Prednisone?
MediHelp also lists interactions of Prednisone with, for example, Bcg vaccine live, Measles vaccine, Mifepristone. The full list is on the Prednisone page.
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