Does the conventional dosage of linezolid necessitate therapeutic drug monitoring?—Experience from a prospective observational study

Background: The objectives of the present prospective observational study conducted in patients receiving conventional dosage of linezolid was to define the pharmacodynamic range of linezolid exposure, to assess the inter-individual variability in linezolid concentrations, and to define if therapeutic drug monitoring (TDM) of linezolid may be necessary for Chinese population. Methods: Patients included in this study underwent linezolid TDM trough concentration (Cmin) during treatment with a standard regimen in the period between January 2019 and October 2019. Linezolid Cmin was analyzed with high-performance liquid chromatography (HPLC) method. Logistic regression was used to define the desired range of linezolid Cmin. Linear regression and univariate logistic regression analysis were carried out to investigate variables associated with inappropriate linezolid plasma exposure. Results: A total of 84 patients who had 153 linezolid Cmin assessed were included in the study. Median linezolid Cmin was 3.43 mg/L (IQR 1.59-5.93). The estimated probability of thrombocytopenia was 50% in the presence of Cmin of 7.85 mg/L. Approximately 57.52% (88/153) of the samples fell within the desired range of linezolid Cmin (2-8 mg/L) while 31.37% (48/153) experienced underexposure, and overexposure occurred in 11.11% (17/153) of the patients. No significant linear relationships between either body weight or estimated creatinine clearance (CrCL) and Cmin were detected. Estimated CrCL ≥100 mL/min was significantly associated with linezolid underexposure (OR 4.121; 95% CI, 1.945-8.731; P<0.001). Estimated CrCL ≤40 mL/min was significantly associated with linezolid overexposure (OR 3.761; 95% CI, 1.324-10.681; P=0.013). Conclusions: Our results suggest that the pharmacodynamic range of linezolid Cmin can be defined as 2-8 mg/L for the Chinese population. Renal function partially accounts for the inter-interindividual variability of exposure. The application of TDM might be especially valuable in optimizing linezolid exposure in the majority of patients to avoid therapeutic failure and/or dose-dependent adverse reactions.