Drug interactions
Fosphenytoin + Imatinib
Severity: Major
Fosphenytoin and Imatinib: 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, which can substantially reduce imatinib concentrations and risk loss of efficacy. Imatinib may in turn raise phenytoin levels, risking phenytoin toxicity given its narrow therapeutic index.
What this interaction means in plain words
Fosphenytoin and Imatinib 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; Imatinib belongs to Oncology.
Why it happens
Phenytoin induces CYP3A4 and increases imatinib clearance, while imatinib may inhibit CYP2C9/2C19-mediated phenytoin metabolism.
What to do
Avoid the combination if possible and use a non-enzyme-inducing antiepileptic; if unavoidable, increase the imatinib dose with monitoring and check phenytoin levels.
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 Imatinib
- Imatinib + Lomitapide Contraindicated
- Imatinib + Lonafarnib Contraindicated
- Amobarbital + Imatinib Major
- Apalutamide + Imatinib Major
- Avapritinib + Imatinib Major
- Benzhydrocodone / acetaminophen + Imatinib 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 Imatinib?
MediHelp rates the interaction as major. Fosphenytoin and Imatinib 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, which can substantially reduce imatinib concentrations and risk loss of efficacy. Imatinib may in turn raise phenytoin levels, risking phenytoin toxicity given its narrow therapeutic index.
How serious is the interaction between Fosphenytoin and Imatinib?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination if possible and use a non-enzyme-inducing antiepileptic; if unavoidable, increase the imatinib dose with monitoring and check phenytoin levels.
What other medicines interact with Imatinib?
MediHelp also lists interactions of Imatinib with, for example, Lomitapide, Lonafarnib, Amobarbital. The full list is on the Imatinib page.
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