Drug interactions
Gefitinib + Phenytoin
Severity: Major
Gefitinib 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 substantially lower gefitinib exposure. This may reduce antitumor efficacy in EGFR-mutated lung cancer.
What this interaction means in plain words
Gefitinib 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.
Gefitinib belongs to Oncology; Phenytoin belongs to Central Nervous System.
Why it happens
CYP3A4 induction by phenytoin accelerates the metabolism of gefitinib.
What to do
Prefer an alternative anticonvulsant without enzyme induction. If unavoidable, increase gefitinib to 500 mg daily and return to 250 mg about 7 days after 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 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 Gefitinib
Frequently asked questions
Can I take Gefitinib with Phenytoin?
MediHelp rates the interaction as major. Gefitinib 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 substantially lower gefitinib exposure. This may reduce antitumor efficacy in EGFR-mutated lung cancer.
How serious is the interaction between Gefitinib 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 an alternative anticonvulsant without enzyme induction. If unavoidable, increase gefitinib to 500 mg daily and return to 250 mg about 7 days after phenytoin is stopped.
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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