Effects of Different Linezolid Concentration Levels on Hematologic Side Effects: A New Target for Therapeutic Drug Monitoring

The emergence of a linezolid minimum inhibitory concentration creep (2-4 mg/L) necessitates higher trough concentrations (Cmin), which may increase the risk of hematological side effects. Evaluating the effects of different linezolid Cmin levels on hematological indices and determining a new target Cmin range are essential. Elderly patients receiving linezolid at 4 tertiary hospitals between May 2021 and March 2024 were grouped according to their Cmin levels. Linezolid Cmin and hematological indices were monitored dynamically. A total of 320 patients were enrolled, and 128 patients were included in the analysis of hematological side effects following propensity score matching between Cmin >16 mg/L and Cmin ≤16 mg/L. The incidence of thrombocytopenia and the reduction in platelet count were significantly greater in patients with Cmin >16 mg/L compared with those with Cmin ≤16 mg/L. However, no significant differences were observed in the incidence of anemia or changes in hemoglobin levels. Among the 96 patients with Cmin ≤16 mg/L, multivariate analysis identified Cmin as an independent risk factor for thrombocytopenia but not for anemia. Furthermore, no significant difference in thrombocytopenia risk was found between patients with Cmin levels of 8-14.5 mg/L and those with Cmin of <8 mg/L (odds ratio, 1.183; 95% confidence interval, 0.428-3.275; P = 0.746). In elderly patients, hematological side effects did not increase with increasing Cmin levels up to 14.5 mg/L. These findings suggest that a target Cmin range of 2-14.5 mg/L may be appropriate for the elderly population receiving linezolid. ChiCTR2100045707; April 23, 2021.