Drug interactions
Fosphenytoin + Vinblastine
Severity: Moderate
Fosphenytoin and Vinblastine: moderate 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
Fosphenytoin is converted to phenytoin, a strong CYP3A4 and P-gp inducer that may lower vinblastine exposure and efficacy. Chemotherapy with vinca alkaloids may also lower phenytoin levels, risking seizure breakthrough.
What this interaction means in plain words
Fosphenytoin and Vinblastine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Fosphenytoin belongs to Central Nervous System; Vinblastine belongs to Oncology.
Why it happens
Phenytoin induces CYP3A4 and P-gp, increasing vinblastine clearance, while chemotherapy may reduce phenytoin levels through poorly defined mechanisms.
What to do
Monitor phenytoin levels and seizure control, and consider a non-enzyme-inducing anticonvulsant such as levetiracetam. Watch for reduced vinblastine response.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Vinblastine
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 Fosphenytoin with Vinblastine?
MediHelp rates the interaction as moderate. Fosphenytoin and Vinblastine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Fosphenytoin is converted to phenytoin, a strong CYP3A4 and P-gp inducer that may lower vinblastine exposure and efficacy. Chemotherapy with vinca alkaloids may also lower phenytoin levels, risking seizure breakthrough.
How serious is the interaction between Fosphenytoin and Vinblastine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor phenytoin levels and seizure control, and consider a non-enzyme-inducing anticonvulsant such as levetiracetam. Watch for reduced vinblastine response.
What other medicines interact with Vinblastine?
MediHelp also lists interactions of Vinblastine with, for example, Adenovirus types 4 and 7 live, Apalutamide, Atazanavir. The full list is on the Vinblastine page.
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