Drug interactions
Capecitabine + Fosphenytoin
Severity: Major
Capecitabine and Fosphenytoin: 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 can raise serum phenytoin concentrations, and fosphenytoin is converted to phenytoin. This may cause toxicity such as nystagmus, ataxia and confusion, with cases of markedly raised levels reported.
What this interaction means in plain words
Capecitabine and Fosphenytoin 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; Fosphenytoin belongs to Central Nervous System.
Why it happens
Probably inhibition of CYP2C9-mediated phenytoin metabolism by fluorinated pyrimidine metabolites; the mechanism is not fully established.
What to do
Check phenytoin levels at baseline and after starting capecitabine, then monitor regularly. Reduce the fosphenytoin dose as needed.
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 Capecitabine
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Capecitabine with Fosphenytoin?
MediHelp rates the interaction as major. Capecitabine and Fosphenytoin 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 can raise serum phenytoin concentrations, and fosphenytoin is converted to phenytoin. This may cause toxicity such as nystagmus, ataxia and confusion, with cases of markedly raised levels reported.
How serious is the interaction between Capecitabine and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check phenytoin levels at baseline and after starting capecitabine, then monitor regularly. Reduce the fosphenytoin dose as needed.
What other medicines interact with Capecitabine?
MediHelp also lists interactions of Capecitabine with, for example, Adenovirus types 4 and 7 live, Arsenic trioxide, Axicabtagene ciloleucel. The full list is on the Capecitabine page.
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