Pharmacokinetic evaluation of linezolid administered intravenously in obese patients with pneumonia

Objectives Altered linezolid pharmacokinetics (PK) in obese individuals has been hypothesized in previous studies. However, specific dosing recommendations for this population are still lacking. The main goal of this study was to evaluate PK/pharmacodynamic (PKPD) target attainment when using a 600mg intravenous q12h linezolid dose against MRSA in obese patients with pneumonia. Methods Fifteen obese pneumonia patients with a confirmed or suspected MRSA involvement treated with 600mg of intravenous linezolid q12h were studied for 3days. Population PK modelling was used to characterize the PK variability and to screen for influential patient characteristics. Monte Carlo simulations were carried out to investigate the PTA and time to target attainment for linezolid dosing against MRSA. Results A two-compartment model with linear elimination adequately described the data. Body weight and age both have a significant effect on linezolid clearance. Simulations demonstrate that the probability of attaining PKPD targets is low. Moreover, the PTA decreases with weight, and increases with age. Standard linezolid dosing in obese pneumonia patients with MRSA (MICs of 1-4mg/L) leads to unacceptably low (near zero to 60%) PTA for patients <65years old. Conclusions Standard linezolid dosing is likely to provide insufficient target attainment against MRSA in obese patients. Body weight and especially age are important characteristics to be considered when administering linezolid to treat MRSA infections.