Drug interactions
Fosphenytoin + Sirolimus
Severity: Major
Fosphenytoin and Sirolimus: 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
Fosphenytoin lowers sirolimus concentrations and may lead to loss of immunosuppressive effect and graft rejection. The effect develops over days to weeks and persists after discontinuation.
What this interaction means in plain words
Fosphenytoin and Sirolimus 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; Sirolimus belongs to Miscellaneous.
Why it happens
Phenytoin induces CYP3A4 and P-glycoprotein, increasing sirolimus clearance.
What to do
Use a non-inducing anticonvulsant when possible. If combined, increase the sirolimus dose guided by trough levels and reassess after stopping fosphenytoin.
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 Sirolimus
- Adenovirus types 4 and 7 live + Sirolimus Contraindicated
- Bcg vaccine live + Sirolimus Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Sirolimus Contraindicated
- Ketoconazole + Sirolimus Contraindicated
- Levoketoconazole + Sirolimus Contraindicated
- Measles mumps and rubella vaccine live + Sirolimus Contraindicated
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 Sirolimus?
MediHelp rates the interaction as major. Fosphenytoin and Sirolimus 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 lowers sirolimus concentrations and may lead to loss of immunosuppressive effect and graft rejection. The effect develops over days to weeks and persists after discontinuation.
How serious is the interaction between Fosphenytoin and Sirolimus?
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 anticonvulsant when possible. If combined, increase the sirolimus dose guided by trough levels and reassess after stopping fosphenytoin.
What other medicines interact with Sirolimus?
MediHelp also lists interactions of Sirolimus with, for example, Adenovirus types 4 and 7 live, Bcg vaccine live, Influenza virus vaccine quadrivalent intranasal. The full list is on the Sirolimus page.
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