Pharmacokinetics of tacrolimus according to body composition in recipients of kidney transplants

BACKGROUND: Currently, the dosage of tacrolimus used after transplantation is based on the patient's body weight. However, there is a low correlation between body weight and body composition in kidney transplant recipients. In this study, we evaluate the pharmacokinetics of tacrolimus according to body composition in 18 Korean kidney transplant recipients with stable graft function. METHODS: Body composition parameters were calculated using bioelectrical impedance analysis. Pharmacokinetic profiles were determined 0, 1, 2, 3, and 4 hours after treatment with tacrolimus and were compared between high- and low-level median body composition groups. The values of C(0), C(1), C(2), C(3), and C(4) were used in determining an abbreviated area under the curve (AUC) for tacrolimus. RESULTS: The mean body mass index (BMI) and body composition values were as follows: BMI, 24.3 kg/m(2); lean mass, 49.8 kg; and fat mass, 17.4 kg. There were no statistical differences in pharmacokinetic profiles between groups with different BMIs. However, the C(0) and C(4) in the high-fat group were significantly elevated compared with those of the low-fat group (P=0.024 and 0.031, respectively). Furthermore, the C(0), C(2), C(3), and C(4) and the AUC were significantly different between the two lean mass groups (P=0.007, 0.038, 0.047, 0.015, and 0.015, respectively). Other variables, such as waist circumference and arm muscle circumference, did not differentiate between the pharmacokinetic profiles of tacrolimus. CONCLUSION: Taken together, these data suggest that tacrolimus dose monitoring based on body composition may provide adequate dosage leading to favorable long-term outcomes.