Stability and Validation of a High-Throughput LC-MS/MS Method for the Quantification of Cefepime, Meropenem, and Piperacillin and Tazobactam in Serum

Background: The class of antibiotics known as β-lactams are a commonly used due to their effectiveness and safety. Therapeutic drug monitoring has been proposed but requires an accurate assay along with well-characterized preanalytic stability, as β-lactams are known to be relatively unstable. Methods: A high-throughput LC-MS/MS assay validation and stability study was performed for cefepime, meropenem, and piperacillin and tazobactam in serum. Patient samples, standards, and QCs were crashed with acetonitrile containing internal standard. Following centrifugation, an aliquot of the supernatant was diluted with clinical laboratory reagent water and analyzed by LC-MS/MS. Results: The assay showed linearity between 0.5 and 60 μg/mL for each analyte. The intra- and interassay reproducibility at 3 different concentrations (approximately 2, 25, and 40 μg/mL) was <5% for each analyte. Accuracy studies for each analyte were compared using linear regression and demonstrated: slope = 1.0 ± 0.1; r2 ≥ 0.980; and y intercept 95% CI that included zero. Minimal ion suppression or enhancement was observed, and no significant carryover was observed up to 500 μg/mL of each analyte. Stability studies demonstrated significant loss in serum for each analyte at ambient and refrigerated temperatures (2-8 °C) and at -20 °C over days or weeks. In contrast, when stored at -80 °C, no significant loss was observed. Conclusions: The LC-MS/MS assay showed acceptable performance characteristics for quantitation of β-lactams. With well-characterized stability, this assay can be used with residual specimens for pharmacokinetic modeling, which may lead to individualized dosing and improved patient care.