Drug interactions
Cyclosporin + Fosphenytoin
Severity: Major
Cyclosporin and Fosphenytoin: 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
Phenytoin, the active metabolite of fosphenytoin, induces CYP3A4 and P-gp and can substantially lower cyclosporine concentrations. This risks transplant rejection or loss of immunosuppressive effect, and cyclosporine levels may rebound when phenytoin is stopped.
What this interaction means in plain words
Cyclosporin and Fosphenytoin 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.
Cyclosporin belongs to Miscellaneous; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4 and P-glycoprotein, increasing cyclosporine clearance.
What to do
Monitor cyclosporine trough levels closely and increase the dose as needed, or use a non-inducing anticonvulsant. Recheck levels when phenytoin is stopped.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Cyclosporin and Fosphenytoin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
References
Other interactions of Cyclosporin
- Adenovirus types 4 and 7 live + Cyclosporin Contraindicated
- Aliskiren + Cyclosporin Contraindicated
- Bcg vaccine live + Cyclosporin Contraindicated
- Bosentan + Cyclosporin Contraindicated
- Cidofovir + Cyclosporin Contraindicated
- Cyclosporin + Dengue vaccine 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 Cyclosporin with Fosphenytoin?
MediHelp rates the interaction as major. Cyclosporin and Fosphenytoin 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, the active metabolite of fosphenytoin, induces CYP3A4 and P-gp and can substantially lower cyclosporine concentrations. This risks transplant rejection or loss of immunosuppressive effect, and cyclosporine levels may rebound when phenytoin is stopped.
How serious is the interaction between Cyclosporin and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor cyclosporine trough levels closely and increase the dose as needed, or use a non-inducing anticonvulsant. Recheck levels when phenytoin is stopped.
What other medicines interact with Cyclosporin?
MediHelp also lists interactions of Cyclosporin with, for example, Adenovirus types 4 and 7 live, Aliskiren, Bcg vaccine live. The full list is on the Cyclosporin page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
