Background: The aim of our work was to develop and validate a reliable LC-MS/MS-based measurement procedure for the quantification of vancomycin in serum, to be applied in the context of efforts to standardize and harmonize therapeutic drug monitoring of this compound using routine assays.

Methods: Sample preparation was based on protein precipitation followed by ultrafiltration. In order to minimize differential modulation of ionization by matrix constituents extended chromatographic separation was applied leading to a retention time of 9.8 min for the analyte. Measurement was done by HPLC-ESI-MS/MS. For internal standardization the derivative vancomycin-glycin (ISTD) prepared by chemical synthesis was used, HPLC conditions ensured coelution of ISTD with the analyte.

Results: In a bi-center validation total CVs of <4% were observed for quality control material ranging from 5.3 mg/L to 79.4 mg/L; accuracy was ±4%. No relevant ion suppression was observed. Comparative measurement of aliquots from 70 samples at the two validation sites demonstrated close agreement.

Conclusions: Employing a closely related homologue molecule for internal standardization and the use of MS/MS following highly efficient sample pre-fractionation by HPLC, the method described here can be considered to offer the highest level of analytical reliability realized so far for the quantification of vancomycin in human serum. Thus, the method is suitable to be used in a comprehensive reference measurement system for vancomycin.