Drug interactions
Fosamprenavir + Siponimod
Severity: Major
Fosamprenavir and Siponimod: 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
Fosamprenavir, whose active metabolite amprenavir is a moderate CYP3A4 inhibitor boosted or not, can raise siponimod exposure. Siponimod is cleared by CYP2C9 and CYP3A4, so a drug that blocks CYP3A4 shifts more of its clearance onto CYP2C9, and this effect is more marked in patients with reduced CYP2C9 function. Higher exposure may increase adverse effects such as bradyarrhythmia, lymphopenia and infection risk.
What this interaction means in plain words
Fosamprenavir and Siponimod 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.
Why it happens
Inhibition of CYP3A4-mediated siponimod metabolism raises siponimod plasma concentrations.
What to do
Avoid combining siponimod with drugs that inhibit both CYP3A4 and CYP2C9 at moderate or greater strength, and check the patient's CYP2C9 genotype before use. If the combination is unavoidable, monitor heart rate, lymphocyte counts and signs of infection closely.
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 Siponimod
- Cladribine + Siponimod Contraindicated
- Fingolimod + Siponimod Contraindicated
- Fluconazole + Siponimod Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Siponimod Contraindicated
- Ponesimod + Siponimod Contraindicated
- Siponimod + Thioridazine Contraindicated
Frequently asked questions
Can I take Fosamprenavir with Siponimod?
MediHelp rates the interaction as major. Fosamprenavir and Siponimod 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. Fosamprenavir, whose active metabolite amprenavir is a moderate CYP3A4 inhibitor boosted or not, can raise siponimod exposure. Siponimod is cleared by CYP2C9 and CYP3A4, so a drug that blocks CYP3A4 shifts more of its clearance onto CYP2C9, and this effect is more marked in patients with reduced CYP2C9 function. Higher exposure may increase adverse effects such as bradyarrhythmia, lymphopenia and infection risk.
How serious is the interaction between Fosamprenavir and Siponimod?
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 combining siponimod with drugs that inhibit both CYP3A4 and CYP2C9 at moderate or greater strength, and check the patient's CYP2C9 genotype before use. If the combination is unavoidable, monitor heart rate, lymphocyte counts and signs of infection closely.
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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