Linezolid continuous infusion protects from subtherapeutic linezolid concentrations in critically ill patients.

Objective: Different studies have determined blood linezolid concentrations. However, the largest studies reporting data on factors associated with subtherapeutic linezolid concentrations in critically ill patients account for less than 60 patients. Thus, the objective of our study was to determine what factors were associated with subtherapeutic linezolid concentrations in critically ill patients in a larger series of patients.

Design: Historical cohort study.

Setting: One Spanish Intensive Care Unit.

Patients: Critically ill adult patients who received linezolid due to suspected or confirmed infection by multidrug-drug-resistant Gram-positive bacteria during 2022 and 2023.

Interventions: Blood samples were collected to determine linezolid concentrations (C_min) immediately before dosing after at least 48 h from starting linezolid therapy.

Main variable of interest: Subtherapeutic linezolid concentrations.

Results: We included a total of 168 patients. We found 79 (47.0%) patients with and 89 (53.0%) patients without subtherapeutic linezolid concentrations. Multiple logistic regression showed that linezolid continuous infusion (OR = 0.192; 95% CI = 0.053-0.694; P = .01) and older age (OR = 0.952; 95% CI = 0.926-0.980; P = .001) were associated with lower risk of subtherapeutic linezolid concentrations.

Conclusions: As far as we know, this is the largest study reporting data on factors associated with subtherapeutic linezolid concentrations in critically ill patients. To our knowledge, our study is the first to report that linezolid continuous infusion was independently associated with lower risk of subtherapeutic linezolid concentrations in critically ill patients.