Drug interactions
Amiodarone + Fosphenytoin
Severity: Major
Amiodarone and Fosphenytoin: 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 can increase phenytoin concentrations after fosphenytoin conversion, leading to toxicity such as ataxia, nystagmus and confusion. Phenytoin is also a CYP3A4 inducer and may lower amiodarone levels, risking loss of arrhythmia control.
What this interaction means in plain words
Amiodarone and Fosphenytoin 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; Fosphenytoin belongs to Central Nervous System.
Why it happens
Amiodarone inhibits CYP2C9/2C19 metabolism of phenytoin, while phenytoin induces CYP3A4 metabolism of amiodarone.
What to do
Measure free or total phenytoin levels when amiodarone is started or stopped and adjust the fosphenytoin dose. Monitor ECG and rhythm control, and check amiodarone effect over several weeks.
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 Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Amiodarone with Fosphenytoin?
MediHelp rates the interaction as major. Amiodarone and Fosphenytoin 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 can increase phenytoin concentrations after fosphenytoin conversion, leading to toxicity such as ataxia, nystagmus and confusion. Phenytoin is also a CYP3A4 inducer and may lower amiodarone levels, risking loss of arrhythmia control.
How serious is the interaction between Amiodarone and Fosphenytoin?
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 free or total phenytoin levels when amiodarone is started or stopped and adjust the fosphenytoin dose. Monitor ECG and rhythm control, and check amiodarone effect over several weeks.
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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