A rapid multiplex LC-MS/MS platform for simultaneous monitoring of eight antibiotics: clinical application and exploratory analysis of determinants of personalized dosing in critically ill patients

Critically ill patients show significant variability in antibiotics pharmacokinetics, often leading to suboptimal dosing and increased risk of treatment failure or toxicity, and the development of drug-resistant bacteria. This study aimed to establish a rapid and reliable LC-MS/MS method for the simultaneous quantification of eight antibiotics (vancomycin, meropenem, linezolid, voriconazole, sulfamethoxazole, trimethoprim, piperacillin, and cefoperazone) in human serum. The secondary aim was to apply this assay to therapeutic drug monitoring (TDM), explore and analyze clinical factors associated with serum drug concentrations, and provide a reference for individualized antibiotic dosing. A multiplex LC-MS/MS method was developed using protein precipitation and validated per FDA/EMA guidelines. It was applied to 522 serum samples from critically ill patients undergoing TDM. Clinical and laboratory data were analyzed using Spearman correlation and multiple linear regression to identify factors affecting drug levels. The method demonstrated good linearity (r² > 0.98), recovery (63.4–110.6%), and minimal matrix effects (89.2–105.2%). Target attainment rates varied from 22.2% to 70.4%. Creatinine clearance negatively correlated with concentrations of vancomycin, meropenem, linezolid, and piperacillin (p < 0.05). Daily dose positively influenced levels of vancomycin, meropenem, sulfamethoxazole, and trimethoprim (p < 0.01). Sex significantly affected sulfamethoxazole, while red blood cells count was inversely correlated with exposure to meropenem and trimethoprim. A robust and rapid LC-MS/MS method was established for the simultaneous TDM of eight antibiotics and was successfully applied to TDM in critically ill patients. Preliminary analyses showed that renal function, dosing regimen, sex, and anemia may be associated with drug exposure in critically ill patients, potentially providing a preliminary basis for future studies on individualized dosing.