Drug interactions
Amiodarone + Phenytoin
Severity: Major
Amiodarone 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
Amiodarone inhibits CYP2C9 and can substantially raise phenytoin levels, causing ataxia, nystagmus and tremor. Phenytoin in turn induces CYP3A4 and can lower amiodarone levels, and the full effect may take weeks because of amiodarone's long half-life.
What this interaction means in plain words
Amiodarone 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.
Amiodarone belongs to Cardiovascular; Phenytoin belongs to Central Nervous System.
Why it happens
Amiodarone inhibits CYP2C9/2C19 metabolism of phenytoin, while phenytoin induces CYP3A4-mediated amiodarone metabolism.
What to do
Measure phenytoin levels before and for several weeks after starting amiodarone, reducing the phenytoin dose as needed. Monitor rhythm control and consider amiodarone levels.
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 Amiodarone
- Amiodarone + Amisulpride Contraindicated
- Amiodarone + Arsenic trioxide Contraindicated
- Amiodarone + Dofetilide Contraindicated
- Amiodarone + Dronedarone Contraindicated
- Amiodarone + Droperidol Contraindicated
- Amiodarone + Eliglustat Contraindicated
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 Amiodarone with Phenytoin?
MediHelp rates the interaction as major. Amiodarone 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. Amiodarone inhibits CYP2C9 and can substantially raise phenytoin levels, causing ataxia, nystagmus and tremor. Phenytoin in turn induces CYP3A4 and can lower amiodarone levels, and the full effect may take weeks because of amiodarone's long half-life.
How serious is the interaction between Amiodarone 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: Measure phenytoin levels before and for several weeks after starting amiodarone, reducing the phenytoin dose as needed. Monitor rhythm control and consider amiodarone levels.
What other medicines interact with Amiodarone?
MediHelp also lists interactions of Amiodarone with, for example, Amisulpride, Arsenic trioxide, Dofetilide. The full list is on the Amiodarone page.
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