Quantification of piperacillin, tazobactam, cefepime, meropenem, ciprofloxacin and linezolid in serum using an isotope dilution UHPLC-MS/MS method with semi-automated sample preparation.

Background: Recent studies have demonstrated highly variable blood concentrations of piperacillin, tazobactam, cefepime, meropenem, ciprofloxacin and linezolid in critically ill patients with a high incidence of sub-therapeutic levels. Consequently, therapeutic drug monitoring (TDM) of these antibiotics has to be considered, requiring robust and reliable routine analytical methods. The aim of the present work was to develop and validate a multi-analyte ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous quantification of the above mentioned antibiotics. Methods: Sample preparation included a manual protein precipitation step followed by two-dimensional ultra high performance liquid chromatography (2D-UHPLC). Corresponding stable isotope-labeled substances were used as internal standards for all of the analytes, with the exception of tazobactam. The injected sample volume was 7 mu L. The run time was 5.0 min. Results: Inaccuracy was <= 8% and imprecision coefficient of variation (CV) was < 9% for all analytes. Only minor matrix effects and negligible carry-over was observed. The method was found to be robust during the validation period. Conclusions: We were able to develop a reliable 2D-UHPLCMS/MS method addressing analytes with highly heterogeneous physico-chemical properties. The novel assay may be an efficient tool for an optimized process workflow in clinical laboratories for important antibiotics in regards to TDM.