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A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of eight beta-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 (R) 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 mu g/mL of the beta-lactam antibiotics, except for doripenem. The lower limit of quantification was 0.005-0.5 mu g/mL, using 50 mu L 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 beta-lactam antibiotics in clinical practice. (C) 2011 Elsevier B.V. All rights reserved.