Individual pharmacokinetic parameter estimation of gentamicin in an obese hemodialysis patient using non-linear mixed effect model.

This study aimed to estimate individual pharmacokinetic (PK) parameters in an obese hemodialysis (HD) patient receiving gentamicin and to assess the impact of obesity on gentamicin clearance (CL). A 53-year-old obese Korean woman underwent HD and received gentamicin. To estimate individual PK parameters, we employed the POSTHOC option using NONMEM^® 7.4.4. A priori model contained HD as a covariate for CL during HD, and creatinine CL (CrCL), normalized by the group mean value from the a priori model, as a covariate for non-HD CL (CLNHD). Individual CLNHD exhibited a substantial reduction from the population CLNHD, with the value corresponding to 36% of the a priori model's population PK (popPK) parameter. The patient's CrCL exceeded the group maximum of the a priori information, suggesting inaccurate renal function representation. After adjusting CrCL to the group mean from the a priori model, the patient's CLNHD was 138% of the population's typical value. The objective function value for each run was 0.53 and -4.49, respectively. The patient's CLNHD was greater than the popPK parameter value but less than the popPK parameter value when estimated using the patient's original CrCL. Meanwhile, another software (Monolix^®; version 2024R1) gave similar results. This study shows the importance of individualized PK parameter estimation, particularly in obese HD patients, and highlights the potential impact of factors including obesity on gentamicin CL.