Clinically significant drug-drug interaction between tacrolimus and phenobarbital: the price we pay.

Purpose: The case of a 57-year-old male who experienced acute renal transplant rejection due to subtherapeutic tacrolimus levels as a result of drug interaction with phenobarbital.

Summary: Drug interactions with tacrolimus due to its metabolism through the CYP 450 3A4 enzymatic pathway have led to several reports of altered tacrolimus levels, which can lead to acute rejection in renal transplant recipients. We describe the case of a 57-year-old male initiated on immunosuppressive therapy with tacrolimus in addition to his anticonvulsant medications.

Conclusion: Upon tacrolimus dose increases, discontinuation of carbamazepine, and minimization of phenobarbital dose, effective tacrolimus trough levels were achieved in our patient. Identification and elimination of such drug-drug interactions is necessary to assure adequate immunosuppression in renal transplant recipients.