Risk factors for a low linezolid trough plasma concentration in acute infections

Abstract

Linezolid is an antibiotic with time-dependent activity, and both the percentage of time that plasma concentrations exceed the MIC and the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC24/MIC ratio) are associated with clinical response. The aim of this study was to analyze the linezolid trough plasma concentration (C min) and to determine factors associated with a Cmin< 2 mg/liter and other clinically relevant thresholds. Characteristics of 78 patients receiving 600 mg/12 h of linezolid with a Cmin determination at the steady state and within the first 10 days of treatment were retrospectively reviewed. Concentrations were measured using high-pressure liquid chromatography. Univariate and multivariate analysis were performed to identify risk factors of low Cmin. A total of 29.5% of patients had a Cmin< 2 mg/liter. The percentage was significantly higher in patients with an estimated glomerular filtration (eGF) > 80 ml/min, in intensive care unit (ICU) patients, and in patients with an infection due to Staphylococcus aureus. The independent predictors of Cmin< 2 mg/liter were an eGF>80 ml/min (odds ratio [OR], 10; 95% confidence interval [CI], 2.732 to 37.037; P=0.001) and infection due to S. aureus (OR, 5.906; 95% CI, 1.651 to 21.126; P=0.006). A linezolid Cmin of < 2 mg/liter was found in 29.5% of cases, and the risk was significantly higher among those with an eGF > 80 ml/min and in infections due to S. aureus. In patients with severe sepsis, a loading dose or continuous infusion and drug monitoring could improve the pharmacodynamic parameters associated with linezolid efficacy. Copyright © 2013, American Society for Microbiology. All Rights Reserved.