Drug interactions
Phenytoin + Vemurafenib
Severity: Major
Phenytoin and Vemurafenib: 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 may lower vemurafenib concentrations and reduce antitumor efficacy. Vemurafenib may also alter phenytoin levels, which is relevant because phenytoin has a narrow therapeutic index.
What this interaction means in plain words
Phenytoin and Vemurafenib 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 belongs to Central Nervous System; Vemurafenib belongs to Oncology.
Why it happens
Phenytoin induces CYP3A4, increasing vemurafenib clearance.
What to do
Avoid strong CYP3A4 inducers where possible and use a non-inducing anticonvulsant; if phenytoin is unavoidable, monitor tumor 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
Other interactions of Vemurafenib
Frequently asked questions
Can I take Phenytoin with Vemurafenib?
MediHelp rates the interaction as major. Phenytoin and Vemurafenib 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 may lower vemurafenib concentrations and reduce antitumor efficacy. Vemurafenib may also alter phenytoin levels, which is relevant because phenytoin has a narrow therapeutic index.
How serious is the interaction between Phenytoin and Vemurafenib?
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 strong CYP3A4 inducers where possible and use a non-inducing anticonvulsant; if phenytoin is unavoidable, monitor tumor 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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