Major
Carbamazepine × tacrolimus
Antiepileptics. Carboxamide derivatives×Calcineurin inhibitor (immunosuppressant)
Mechanism
Carbamazepine strongly induces CYP3A4 and P-glycoprotein. Tacrolimus plasma levels fall 2- to 3-fold; immunosuppression is lost, raising rejection risk.
Symptoms
Rejection symptoms depend on the organ: fever, graft tenderness, rising creatinine (kidney); jaundice and rising liver enzymes (liver). Symptoms appear 1–3 weeks after starting carbamazepine.
Management
Avoid the combination. Alternative anticonvulsants without induction: levetiracetam, lamotrigine, gabapentin. If carbamazepine is unavoidable, raise tacrolimus 2- to 3-fold with trough (C0) twice weekly.