Drug interactions
Fostamatinib + Phenytoin
Severity: Major
Fostamatinib and Phenytoin: 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
Phenytoin may lower exposure to R406, the active metabolite of fostamatinib, because of CYP3A4 induction. Platelet response in immune thrombocytopenia may be reduced as a result. Labeling advises against use with strong CYP3A4 inducers.
What this interaction means in plain words
Fostamatinib and Phenytoin 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.
Fostamatinib belongs to Oncology; Phenytoin belongs to Central Nervous System.
Why it happens
Enzyme induction of CYP3A4 by phenytoin increases clearance of the active metabolite R406.
What to do
Avoid concurrent use where an alternative antiseizure drug is possible. If used together, monitor platelet counts closely and review fostamatinib efficacy.
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 Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Other interactions of Fostamatinib
- Colchicine + Fostamatinib Major
- Amobarbital + Fostamatinib Moderate
- Apalutamide + Fostamatinib Moderate
- Atorvastatin + Fostamatinib Moderate
- Bosentan + Fostamatinib Moderate
- Carbamazepine + Fostamatinib Moderate
Frequently asked questions
Can I take Fostamatinib with Phenytoin?
MediHelp rates the interaction as major. Fostamatinib and Phenytoin 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 may lower exposure to R406, the active metabolite of fostamatinib, because of CYP3A4 induction. Platelet response in immune thrombocytopenia may be reduced as a result. Labeling advises against use with strong CYP3A4 inducers.
How serious is the interaction between Fostamatinib and Phenytoin?
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 concurrent use where an alternative antiseizure drug is possible. If used together, monitor platelet counts closely and review fostamatinib efficacy.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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