Drug interactions
Fosphenytoin + Sunitinib
Severity: Major
Fosphenytoin and Sunitinib: 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
Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer that can substantially lower sunitinib and active metabolite exposure. This may lead to loss of antitumor efficacy.
What this interaction means in plain words
Fosphenytoin and Sunitinib 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; Sunitinib belongs to Oncology.
Why it happens
Phenytoin induces CYP3A4, accelerating sunitinib metabolism.
What to do
Use a non-inducing antiepileptic where possible. If it cannot be avoided, a sunitinib dose increase may be needed per labeling, with monitoring for toxicity and response.
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 Sunitinib
- Adagrasib + Sunitinib Major
- Amiodarone + Sunitinib Major
- Amisulpride + Sunitinib Major
- Anagrelide + Sunitinib Major
- Apalutamide + Sunitinib Major
- Arsenic trioxide + Sunitinib 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 Sunitinib?
MediHelp rates the interaction as major. Fosphenytoin and Sunitinib 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 is converted to phenytoin, a strong CYP3A4 inducer that can substantially lower sunitinib and active metabolite exposure. This may lead to loss of antitumor efficacy.
How serious is the interaction between Fosphenytoin and Sunitinib?
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-inducing antiepileptic where possible. If it cannot be avoided, a sunitinib dose increase may be needed per labeling, with monitoring for toxicity and response.
What other medicines interact with Sunitinib?
MediHelp also lists interactions of Sunitinib with, for example, Adagrasib, Amiodarone, Amisulpride. The full list is on the Sunitinib page.
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