Simultaneous Measurement of Piperacillin, Tazobactam and Meropenem in Patient Samples Using LC-MS/MS to Support β-Lactam Therapeutic Drug Monitoring

Abstract

Background: Accurate therapeutic drug monitoring (TDM) of β-lactam antibiotics such as meropenem and piperacillin–tazobactam is essential in critically ill patients, where profound pharmacokinetic variability may lead to subtherapeutic exposure or toxicity. Practical, high-throughput analytical workflows are needed to support timely dose optimisation in routine clinical settings. Methods: We developed and fully validated a unified LC–MS/MS method for the simultaneous quantification of meropenem, piperacillin, and tazobactam in human serum. Samples were prepared by protein precipitation and analysed on a C18 column using a water/methanol gradient with 0.1% formic acid. Detection was performed by multiple reaction monitoring with isotopically labelled internal standards. Results: The assay demonstrated excellent linearity (R² > 0.998), high sensitivity (LLOQ 0.02 mg L⁻¹), and robust intra- and inter-day precision (<10%), with a 10 min run time and no detectable carry-over. The method demonstrates high analytical sensitivity, with a lower limit of quantification (LLOQ) of 0.02 mg L⁻¹ for all analytes, which is among the lowest reported for simultaneous quantification of meropenem, piperacillin, and tazobactam. Application to >40 clinical samples from critically ill patients revealed wide concentration ranges (meropenem 0.2–270 mg L⁻¹; piperacillin 1–580 mg L⁻¹; tazobactam 0.1–60 mg L⁻¹), with unbound fractions consistent with published data. Conclusions: This streamlined, low-volume LC–MS/MS workflow enables rapid, accurate quantification of key β-lactam antibiotics and supports routine TDM in critically ill and paediatric populations, facilitating more individualised antimicrobial dosing in clinical practice. Since our method already accommodates β-lactams and a β-lactamase inhibitor with highly heterogeneous physicochemical properties, it provides a robust basis for extending the approach to additional antibiotics within a multi-analyte framework.