Effect of obesity on the population pharmacokinetics of meropenem in critically ill patients

Severe pathophysiological changes in critical illness can lead to dramatically altered antimicrobial pharmacokinetics (PK). The additional effect of obesity on PK potentially increases the challenge for effective dosing. The aim of this prospective study was to describe the population PK of meropenem for a cohort of critically ill patients, including obese and morbidly obese patients. Critically ill patients prescribed meropenem were recruited into the following three body mass index (BMI) groups: nonobese (18.5 to 29.9 kg/m 2 ), obese (30.0 to 39.9 kg/m 2 ), and morbidly obese (≥40 kg/m 2 ). Serial plasma samples were taken, and meropenem concentrations were determined using a validated chromatographic method. Population PK analysis and Monte Carlo dosing simulations were undertaken with Pmetrics. Nineteen critically ill patients with different BMI categories were enrolled. The patients' mean ± standard deviation (SD) age, weight, and BMI were 49 ± 15.9 years, 95 ± 22.0 kg, and 33 ± 7.0 kg/m 2 , respectively. A two-compartment model described the data adequately. The mean ± SD parameter estimates for the final covariate model were as follows: clearance (CL), 15.5 ± 6.0 liters/h; volume of distribution in the central compartment (V 1 ), 11.7 ± 5.8 liters; intercompartmental clearance from the central compartment to the peripheral compartment, 25.6 ± 35.1 liters h -1 ; and intercompartmental clearance from the peripheral compartment to the central compartment, 8.32 ± 12.24 liters h -1 . Higher creatinine clearance (CL CR ) was associated with a lower probability of target attainment, with BMI having little effect. Although obesity was found to be associated with an increased V 1 , dose adjustment based on CL CR appears to be more important than patient BMI.