A large variation in the levels of different ß-lactams and other antibiotics used in critically ill patients has been documented. The aim of this study is to establish and validate a fast, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous analysis of ten antibiotics (Meropenem, Cefepime, Ceftazidime, Piperacillin, Benzylpenicillin, Ampicillin, Flucloxacillin, Linezolid, and Sulfamethoxazole/Trimethoprim) in human plasma according to European Medicines Agency (EMA) guidelines. Protein precipitation with ice-cold methanol containing 9 isotopically labeled internal standards was used for sample clean up. Antibiotics were detected, following a 4-minute gradient separation, in multiple reactions monitoring (MRM) using API 4000 instrument equipped with electrospray source operating in positive ion mode. The lower limit of quantification was 0.1 mg/L for Meropenem, Ceftazidime, Piperacillin, Ampicillin, Flucloxacillin, and Sulfamethoxazole; 0.05 mg/L for Cefepime, Benzylpenicillin, and Trimethoprim; and 0.02 mg/L for Linezolid. The method proved to be precise and accurate and applicable for therapeutic drug monitoring and other pharmacokinetic studies.

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