Drug interactions
Felodipine + Phenytoin
Severity: Major
Felodipine and Phenytoin: 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
Phenytoin strongly induces CYP3A4 and can markedly lower felodipine plasma concentrations, leading to loss of antihypertensive or antianginal effect. The reduction can be large enough to make felodipine ineffective.
What this interaction means in plain words
Felodipine and Phenytoin 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.
Felodipine belongs to Cardiovascular; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces hepatic and intestinal CYP3A4, increasing the first-pass and systemic metabolism of felodipine.
What to do
Prefer a calcium channel blocker or antihypertensive not dependent on CYP3A4 if phenytoin is needed. If combined, monitor blood pressure and heart rate and titrate felodipine upward as needed, reassessing when phenytoin 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 Felodipine
- Felodipine + Itraconazole Contraindicated
- Aldesleukin + Felodipine Major
- Amifostine + Felodipine Major
- Apalutamide + Felodipine Major
- Atazanavir + Felodipine Major
- Carbamazepine + Felodipine 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 Felodipine with Phenytoin?
MediHelp rates the interaction as major. Felodipine and Phenytoin 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 strongly induces CYP3A4 and can markedly lower felodipine plasma concentrations, leading to loss of antihypertensive or antianginal effect. The reduction can be large enough to make felodipine ineffective.
How serious is the interaction between Felodipine and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Prefer a calcium channel blocker or antihypertensive not dependent on CYP3A4 if phenytoin is needed. If combined, monitor blood pressure and heart rate and titrate felodipine upward as needed, reassessing when phenytoin is stopped.
What other medicines interact with Felodipine?
MediHelp also lists interactions of Felodipine with, for example, Itraconazole, Aldesleukin, Amifostine. The full list is on the Felodipine page.
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