Development and validation of a simple and sensitive LC-MS/MS method for quantification of ampicillin and sulbactam in human plasma and its application to a clinical pharmacokinetic study

Ampicillin-sulbactam is a broad-spectrum combination antibiotic used for a variety of clinical applications, including as a prophylactic agent to reduce the risk of surgical site infection. The pharmacokinetics of ampicillin-sulbactam after redosing during prolonged surgeries remains incompletely understood. In anticipation of further studying the intra-operative pharmacokinetics of this drug, we have developed a novel liquid chromatography-tandem mass spectrometry (LC–MS/MS) method for the quantification of ampicillin and sulbactam. The plasma samples were prepared using a simple protein precipitation method. Gradient chromatographic elution was used to separate analytes, and MS/MS analysis was performed in negative ionization mode for both analytes via multiple reaction monitoring (MRM). All validation parameters were evaluated under a good laboratory practice (GLP) environment. For both ampicillin and sulbactam, the lower limit of quantitation (LLOQ) was established as 0.25 μg/mL. The calibration curve ranged from 0.25 to 200 μg/mL for ampicillin and 0.25–100 μg/mL for sulbactam. Inter- and intra-day precisions for both analytes were ≤11.5 % for quality controls and ≤17.4 % for LLOQ; accuracies ranged from -11.5 to 12.5% for 3 quality control levels and -18.1–18.7% for LLOQ. In addition to sensitivity, accuracy and precision, 13 other parameters were also validated for both analytes, and the results met the acceptance criteria. Our method was successfully applied to quantify ampicillin and sulbactam concentrations in patients undergoing surgery.