Simultaneous determination of eight β-lactam antibiotics in human serum by liquid chromatography–tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for the simultaneous determination of eight β-lactam antibiotics, including ampicillin, cefazolin, cefepime, cefmetazole, cefotaxime, doripenem, meropenem, and piperacillin, in human serum. Sample specimens were subjected to solid phase extraction (SPE) using Waters Oasis® HLB cartridges (30 mg). Chromatographic separation was performed with a high-resolution octadecyl silica column compatible with hydrophilic compounds, using a gradient of 10 mM aqueous ammonium formate containing 0.1% formic acid-methanol. Antibiotics were detected by a triple quadrupole mass spectrometer (MS/MS) with electrospray ionization and quantified by the multiple reaction monitoring mode. A total run time of 13 min was applied. Linearity in the calibration was obtained over a range of 0.1–50 μg/mL of the β-lactam antibiotics, except for doripenem. The lower limit of quantification was 0.005–0.5 μg/mL, using 50 μL serum. The recovery rate exceeded 80.2% for these analytes, except for doripenem (49.1%) and meropenem (62.3%). The present method is applicable to routine therapeutic monitoring of β-lactam antibiotics in clinical practice.