MajorAntiepileptic, hydantoin derivative (sodium channel blocker)×Calcineurin inhibitor (immunosuppressant)
Updated · Methodology
Mechanism
Phenytoin induces CYP3A4. Tacrolimus level falls 2–3 fold with transplant rejection risk.
Symptoms
Tacrolimus trough below target, laboratory signs of rejection.
Management
For post-transplant epilepsy: levetiracetam or lacosamide as alternative. If phenytoin is needed, increase tacrolimus 2–3 fold with frequent monitoring.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- FDA: Dilantin (phenytoin) prescribing information (2011)– ; DailyMed setid 86dd27d1-9cee-48ae-b55d-e2d2f7dbc593
- AEMPS: Ficha técnica: Tacrolimus (nº registro 84607), sección 4.4 (2026)– AEMPS, CIMA, nº registro 84607, revisión 03/2026, sección 4.4