Background. Tacrolimus, an immunosuppressive agent, is widely used in patients after transplantation to prevent allograft rejection. Because tacrolimus has a narrow therapeutic range, it is essential to carefully control the blood level. It has been demonstrated that tacrolimus is metabolized mainly by cytochrome P-450 (CYP) 3A4, and that tacrolimus is a substrate of P-glycoprotein. Methods. This article reports a case of considerable increase in the blood level of tacrolimus after the intake of pomelo in a renal transplant recipient. Results. Pomelo may increase the blood concentration of tacrolimus by inhibiting CYP 3A4, P-glycoprotein, or both. Conclusions. Patients taking drugs such as tacrolimus or cyclosporine, which have their kinetics affected by grapefruit juice, should avoid pomelo and other grapefruit-related citrus fruits.
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