Drug interactions
Diltiazem + Phenytoin
Severity: Moderate
Diltiazem and Phenytoin: 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 induces hepatic and intestinal enzymes and can lower diltiazem concentrations, potentially reducing its antihypertensive, antianginal or rate-control effect. Diltiazem may also raise phenytoin levels in some patients.
What this interaction means in plain words
Diltiazem and Phenytoin 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.
Diltiazem belongs to Cardiovascular; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing diltiazem metabolism, while diltiazem may inhibit phenytoin metabolism.
What to do
Monitor heart rate, blood pressure and angina or arrhythmia control, and increase the diltiazem dose if needed. Check phenytoin levels and watch for toxicity when diltiazem is started or stopped.
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 Diltiazem
- Diltiazem + Flibanserin Contraindicated
- Diltiazem + Ivabradine Contraindicated
- Diltiazem + Lomitapide Contraindicated
- Diltiazem + Lonafarnib Contraindicated
- Acebutolol + Diltiazem Major
- Alfentanil + Diltiazem 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 Diltiazem with Phenytoin?
MediHelp rates the interaction as moderate. Diltiazem and Phenytoin 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 induces hepatic and intestinal enzymes and can lower diltiazem concentrations, potentially reducing its antihypertensive, antianginal or rate-control effect. Diltiazem may also raise phenytoin levels in some patients.
How serious is the interaction between Diltiazem and Phenytoin?
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 heart rate, blood pressure and angina or arrhythmia control, and increase the diltiazem dose if needed. Check phenytoin levels and watch for toxicity when diltiazem is started or stopped.
What other medicines interact with Diltiazem?
MediHelp also lists interactions of Diltiazem with, for example, Flibanserin, Ivabradine, Lomitapide. The full list is on the Diltiazem page.
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