Drug interactions
Capecitabine + Phenytoin
Severity: Major
Capecitabine 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
Capecitabine has been associated with raised phenytoin levels and phenytoin toxicity such as ataxia, nystagmus and confusion. Reports suggest the effect can be substantial.
What this interaction means in plain words
Capecitabine 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.
Capecitabine belongs to Oncology; Phenytoin belongs to Central Nervous System.
Why it happens
Fluorouracil from capecitabine is thought to inhibit CYP2C9-mediated phenytoin metabolism.
What to do
Measure phenytoin levels before and during capecitabine and reduce the phenytoin dose as indicated. Watch for signs of toxicity.
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 Capecitabine
Frequently asked questions
Can I take Capecitabine with Phenytoin?
MediHelp rates the interaction as major. Capecitabine 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. Capecitabine has been associated with raised phenytoin levels and phenytoin toxicity such as ataxia, nystagmus and confusion. Reports suggest the effect can be substantial.
How serious is the interaction between Capecitabine 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: Measure phenytoin levels before and during capecitabine and reduce the phenytoin dose as indicated. Watch for signs of toxicity.
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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