Circadian variability of pharmacokinetics of cisplatin in patients with non-small-cell lung carcinoma: analysis with the NONMEM program.

The aim of this study was to describe the nonlinear pharmacokinetics of total and unbound plasma cisplatin under different administered time in patients with non-small-cell lung carcinoma. Patients receiving chemotherapy with cisplatin were included in this analysis. Patients were divided into two groups depending on the administrated time of cisplatin: 6:00 (Group A) and 18:00 (Group B). The population pharmacokinetics of cisplatin was calculated using nonlinear mixed-effects modeling (NONMEM) method, and the possible influence of covariates on the population pharmacokinetics of cisplatin was also explored. The pharmacokinetics of total and unbound cisplatin could be described well by a linear two-compartment model. The mean population estimates for total and unbound drug were, respectively, 0.463 (17.0 %) and 25.4 (14.0 %) l h⁻¹ for clearance (CL), 24.2 (19.9 %) and 20.5 (27.1 %) l for central distribution volume (V₁), 10.2 (18.2 %) and 9.82 (28.1) l h⁻¹ for intercompartmental clearance (Q) and 32.0 (24.1 %) and 6.77 (25.4 %) l for peripheral compartment volume (V₂). The CL for total and unbound cisplatin was dependent on body surface area (BSA). When cisplatin was administered at 18:00, the CL was 1.38- and 1.22-fold higher than those administered at 6:00 for total and unbound cisplatin, respectively (P < 0.05). The mean parameter estimates from a nonparametric bootstrap procedure were comparable and within 5 % of the estimates from NONMEM. The results showed that circadian could influence the metabolism of cisplatin and suggested the conventional dose adjustment of cisplatin based on BSA.