Drug interactions
Fostamatinib + Siponimod
Severity: Moderate
Fostamatinib and Siponimod: 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
Fostamatinib's active metabolite R406 is a weak CYP3A4 inhibitor, so it may modestly raise siponimod levels. The clinical effect is probably small unless CYP2C9 function is also impaired. Greater exposure could add to bradycardia and lymphopenia.
What this interaction means in plain words
Fostamatinib and Siponimod 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.
Fostamatinib belongs to Oncology; Siponimod belongs to Central Nervous System.
Why it happens
Weak CYP3A4 inhibition by the active metabolite R406 may slightly reduce siponimod metabolism.
What to do
Check CYP2C9 genotype and avoid the combination in poor metabolizers or when a CYP2C9 inhibitor is also present. Otherwise monitor heart rate and lymphocyte counts.
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 Siponimod
- Cladribine + Siponimod Contraindicated
- Fingolimod + Siponimod Contraindicated
- Fluconazole + Siponimod Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Siponimod Contraindicated
- Ponesimod + Siponimod Contraindicated
- Siponimod + Thioridazine Contraindicated
Other interactions of Fostamatinib
- Colchicine + Fostamatinib Major
- Fostamatinib + Phenytoin Major
- Amobarbital + Fostamatinib Moderate
- Apalutamide + Fostamatinib Moderate
- Atorvastatin + Fostamatinib Moderate
- Bosentan + Fostamatinib Moderate
Frequently asked questions
Can I take Fostamatinib with Siponimod?
MediHelp rates the interaction as moderate. Fostamatinib and Siponimod 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. Fostamatinib's active metabolite R406 is a weak CYP3A4 inhibitor, so it may modestly raise siponimod levels. The clinical effect is probably small unless CYP2C9 function is also impaired. Greater exposure could add to bradycardia and lymphopenia.
How serious is the interaction between Fostamatinib and Siponimod?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check CYP2C9 genotype and avoid the combination in poor metabolizers or when a CYP2C9 inhibitor is also present. Otherwise monitor heart rate and lymphocyte counts.
What other medicines interact with Siponimod?
MediHelp also lists interactions of Siponimod with, for example, Cladribine, Fingolimod, Fluconazole. The full list is on the Siponimod page.
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