Therapeutic drug monitoring of free vancomycin concentration in practice: A new analytical technique based on the HFCF–UF sample separation method

The aim of this study was to establish a method for free vancomycin concentration determination in human plasma and apply it to clinical therapeutic drug monitoring (TDM). The unbound vancomycin in plasma was separated by the hollow fiber centrifugal ultrafiltration (HFCF-UF) technique and analyzed by HPLC. Chromatographic conditions were optimized, the specificity, linearity, precision, recovery and stability of the method were examined, and plasma samples of patients were measured. The standard curve for free vancomycin is y = 0.0277x - 0.0080 with good linearity within 0.25-50 μg·mL-1 . The relative and absolute recovery rates for vancomycin were 98.63-101.0% and 88.41-101.2%, respectively. The intraday and interday precision RSDs were <10%. Plasma was stable under several conditions. The TDM value of the free vancomycin concentration of 20 patients was 0.99-38.51 μg·mL-1 , and the correlation between the free and total concentrations was not significant. The unbound fraction of vancomycin ranged from 25.5 to 84.8%, with large variation. The operation of free vancomycin separation by HFCF-UF was simple and suitable for TDM in practice. The unbound fraction of vancomycin in clinical samples varied significantly between individuals. It is recommended to perform free concentration TDM in critically ill patients.