Drug interactions
Fosphenytoin + Vincristine
Severity: Major
Fosphenytoin and Vincristine: major interaction.
Last updated Sources: US FDA label
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, the active metabolite of fosphenytoin, induces CYP3A4 and can lower vincristine exposure, possibly reducing antitumor efficacy. Chemotherapy including vincristine may in turn lower phenytoin levels and risk seizures.
What this interaction means in plain words
Fosphenytoin and Vincristine 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.
Fosphenytoin belongs to Central Nervous System; Vincristine belongs to Oncology.
Why it happens
Phenytoin induction of CYP3A4 increases vincristine clearance, while chemotherapy may reduce phenytoin levels.
What to do
Use a non-enzyme-inducing antiseizure drug such as levetiracetam where possible. If fosphenytoin is needed, monitor phenytoin levels and seizure control and watch for reduced vincristine effect.
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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References
Other interactions of Vincristine
- Adenovirus types 4 and 7 live + Vincristine Contraindicated
- Apalutamide + Vincristine Major
- Atazanavir + Vincristine Major
- Ceritinib + Vincristine Major
- Chloramphenicol + Vincristine Major
- Clarithromycin + Vincristine Major
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 Vincristine?
MediHelp rates the interaction as major. Fosphenytoin and Vincristine 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, the active metabolite of fosphenytoin, induces CYP3A4 and can lower vincristine exposure, possibly reducing antitumor efficacy. Chemotherapy including vincristine may in turn lower phenytoin levels and risk seizures.
How serious is the interaction between Fosphenytoin and Vincristine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use a non-enzyme-inducing antiseizure drug such as levetiracetam where possible. If fosphenytoin is needed, monitor phenytoin levels and seizure control and watch for reduced vincristine effect.
What other medicines interact with Vincristine?
MediHelp also lists interactions of Vincristine with, for example, Adenovirus types 4 and 7 live, Apalutamide, Atazanavir. The full list is on the Vincristine page.
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