Drug interactions
Ivacaftor + Phenytoin
Severity: Major
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
Strong CYP3A4 inducers markedly reduce ivacaftor exposure, which may lead to loss of CFTR potentiation and loss of clinical benefit. Phenytoin is expected to behave similarly.
What this interaction means in plain words
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.
Ivacaftor belongs to Miscellaneous; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, greatly increasing ivacaftor metabolism.
What to do
Avoid coadministration and choose a non-inducing antiseizure drug. Monitor lung function if it cannot be avoided.
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
Other interactions of Ivacaftor
- Ensitrelvir + Ivacaftor Contraindicated
- Apalutamide + Ivacaftor Major
- Carbamazepine + Ivacaftor Major
- Clarithromycin + Ivacaftor Major
- Efavirenz + Ivacaftor Major
- Enzalutamide + Ivacaftor Major
Frequently asked questions
Can I take Ivacaftor with Phenytoin?
MediHelp rates the interaction as major. 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. Strong CYP3A4 inducers markedly reduce ivacaftor exposure, which may lead to loss of CFTR potentiation and loss of clinical benefit. Phenytoin is expected to behave similarly.
How serious is the interaction between 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 coadministration and choose a non-inducing antiseizure drug. Monitor lung function if it cannot be avoided.
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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