RESUMO
WHAT IS KNOWN AND OBJECTIVE: Tacrolimus, the most widely used calcineurin inhibitor in kidney transplantation, has a narrow therapeutic window with high interindividual variability in its pharmacokinetics. Clinically feasible models that combine important factors may help guide individual tacrolimus dosage adjustment in kidney transplant patients. The purpose of this study was to develop a population pharmacokinetic model and investigate the influence of clinical factors on the pharmacokinetics of tacrolimus in adult Thai kidney transplant patients from routine data monitoring. METHODS: A total of 1183 whole blood concentrations from 96 patients were characterized using nonlinear mixed-effects modelling. Clinical factors tested for influence on pharmacokinetic parameters were weight, haemoglobin, duration of tacrolimus therapy, prednisolone dose, serum albumin and estimated glomerular filtration rate. RESULTS AND DISCUSSION: A one-compartment model with first-order absorption best described the data. The population estimate of tacrolimus apparent clearance (CL/F) and apparent volume of distribution (V/F) in the final population model was 21·5 L/h (95% CI; 18·38, 24·34) and 333 L (95% CI; 222·66, 484·35), respectively. CL/F increased with decreasing haemoglobin levels and decreased with increasing duration of tacrolimus therapy (both P < 0·001). The population pharmacokinetic equation that predicted CL/F of tacrolimus was CL/F = 21·5 × exp((-0·05 () (HB) ( - 11·8))) × (DOT/125)(-0·06) , where CL/F was tacrolimus apparent oral clearance (L/h), HB was haemoglobin levels (g/dL), and DOT was duration of tacrolimus therapy (days). No covariates significantly influenced V/F. WHAT IS NEW AND CONCLUSION: The first population pharmacokinetic model of tacrolimus in Thai adult kidney transplant patients was developed and validated. Haemoglobin and duration of tacrolimus therapy could partly explain the interindividual variability in the apparent clearance of tacrolimus. This manuscript also provides a summary review of previously reported population pharmacokinetic models of twice daily tacrolimus in adult kidney transplant recipients.
