MSACL 2023 Abstract

INTRODUCTION: Adequate antibiotic dosage is a prerequisite for the successful treatment of bacterial infections. The pharmacokinetics of antibacterial drugs in critically ill patients can be dramatically altered by multiple factors such as large volume infusions, organ dysfunction, attenuated renal elimination, hypoproteinemia, and drug interactions. Therapeutic drug monitoring (TDM) of antibacterials can be used to optimize antimicrobial therapy regimens and improve clinical outcome. β-lactam antibiotics are the most commonly used treatments for bacterial infections in intensive care units (ICUs). Thus, there is an interest in determining the plasma concentrations of meropenem and piperacillin/tazobactam to assess the potential added value of using TDM in an ICU setting.

OBJECTIVES: Here, our goal was to develop and validate a clinical liquid chromatography mass spectrometry (LC-MS) assay for the quantitation of meropenem and piperacillin/tazobactam which are commonly used in ICUs.

METHODS: Patient plasma samples were mixed with isotopically labeled internal standards in acetonitrile, centrifuged, and an aliquot of the supernatant was diluted with deionized water and used for injection. LC-multiple reaction monitoring (MRM)-MS analysis was performed on a Shimadzu Nexera XR UHPLC system coupled to the Sciex QTrap 6500+ mass spectrometer operating in the positive ion mode. The column oven temperature was maintained at 40°C. Chromatographic separation was done using a Zorbax Rapid Resolution High Definition Eclipse Plus C18 reversed phase column (2.1 x 50 mm, 1.8-Micron, Agilent). Mobile phases were 0.1% formic acid in water and 0.1% formic acid in acetonitrile. A gradient of 5-95% B over 3 minutes (with a total run time of 6 minutes) was used. The quantitation was performed based on the chromatographic peak area ratios between the analytes and the corresponding internal standards, using Analyst software (Sciex).

RESULTS: A multiplexed assay was developed, capable of simultaneously measuring meropenem, piperacillin, and tazobactam β-lactams in human plasma samples. The method is currently undergoing validation based on the CLSI guidelines, including accuracy/trueness, imprecision, sensitivity, specificity, carryover, stability, and linearity. Preliminary validation results already indicate that the method will successfully meet the required criteria. Several batches of 10-20 ICU patient samples have been analyzed. The method allows the measurement of the plasma concentrations of these antibiotics with a short turnaround time. Overall analysis time from receiving samples to the reporting values was about 1.5 hours for a batch of 10 samples. The turnaround time obtained is satisfactory for the timely adjustment of ICU-patient treatment.

CONCLUSION: LC-MS method for the determination of meropenem and piperacillin/tazobactam antibiotics was established and used for the analysis of ICU patient samples. The analysis has a short turnaround time and is applicable for clinical testing in ICU settings.