Drug interactions
Fosphenytoin + Tacrolimus
Severity: Major
Fosphenytoin and Tacrolimus: 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 form of fosphenytoin, induces CYP3A4 and P-gp and can markedly lower tacrolimus concentrations, risking graft rejection. Tacrolimus may also alter phenytoin levels.
What this interaction means in plain words
Fosphenytoin and Tacrolimus 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; Tacrolimus belongs to Miscellaneous.
Why it happens
Phenytoin induces CYP3A4 and P-gp, increasing tacrolimus clearance and reducing absorption.
What to do
Monitor tacrolimus troughs frequently and increase the dose as needed, or use a non-inducing anticonvulsant; also monitor phenytoin levels.
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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References
Other interactions of Tacrolimus
- Adenovirus types 4 and 7 live + Tacrolimus Contraindicated
- Bcg vaccine live + Tacrolimus Contraindicated
- Cidofovir + Tacrolimus Contraindicated
- Cyclosporin + Tacrolimus Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Tacrolimus Contraindicated
- Measles mumps and rubella vaccine live + Tacrolimus 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 Tacrolimus?
MediHelp rates the interaction as major. Fosphenytoin and Tacrolimus 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 form of fosphenytoin, induces CYP3A4 and P-gp and can markedly lower tacrolimus concentrations, risking graft rejection. Tacrolimus may also alter phenytoin levels.
How serious is the interaction between Fosphenytoin and Tacrolimus?
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 tacrolimus troughs frequently and increase the dose as needed, or use a non-inducing anticonvulsant; also monitor phenytoin levels.
What other medicines interact with Tacrolimus?
MediHelp also lists interactions of Tacrolimus with, for example, Adenovirus types 4 and 7 live, Bcg vaccine live, Cidofovir. The full list is on the Tacrolimus page.
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