Drug interactions
Lumacaftor / ivacaftor + Phenytoin
Severity: Major
Lumacaftor / ivacaftor 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 lowers ivacaftor exposure and may weaken the cystic fibrosis response. Lumacaftor itself is an inducer, which complicates phenytoin levels too.
What this interaction means in plain words
Lumacaftor / ivacaftor 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.
Why it happens
Phenytoin induces CYP3A4, which metabolizes ivacaftor.
What to do
Avoid the combination if possible; use a non-inducing anticonvulsant. If used, monitor clinical response and phenytoin 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 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 Lumacaftor / ivacaftor with Phenytoin?
MediHelp rates the interaction as major. Lumacaftor / ivacaftor 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 lowers ivacaftor exposure and may weaken the cystic fibrosis response. Lumacaftor itself is an inducer, which complicates phenytoin levels too.
How serious is the interaction between Lumacaftor / ivacaftor 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: Avoid the combination if possible; use a non-inducing anticonvulsant. If used, monitor clinical response and phenytoin levels.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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