An isotope dilution-liquid chromatography-tandem mass spectrometry-based candidate reference measurement procedure for the quantification of piperacillin in human serum and plasma.

OBJECTIVES: Piperacillin is a broad-spectrum antibiotic used to treat critically ill patients with severe infections, requiring therapeutic drug monitoring (TDM). We report the development of an isotope dilution-liquid chromatography-tandem mass spectrometry-based candidate reference measurement procedure (RMP) to quantify piperacillin in human plasma and serum. METHODS: Primary reference material was characterized by quantitative nuclear magnetic resonance (qNMR) to ensure traceability to the International System of Units (SI). Piperacillin was analyzed using LC-MS/MS operating in positive electrospray ionization and multiple reaction monitoring mode. Method validation evaluated selectivity, matrix effects, precision, accuracy, and measurement uncertainty (MU) according to GUM guidelines. RESULTS: This RMP allowed quantification of piperacillin within the range of 0.773 µmol/L (0.400 µg/mL) to 464 µmol/L (240 µg/mL), with selectivity, sensitivity and matrix-independence. Intermediate precision was <2.3 % and <1.1 % for spiked analyte in free human serum and native patient pools, respectively. The repeatability CV ranged from 0.7 to 2.0 % and relative mean bias ranged from -1.5 to 2.9 % across matrices and concentrations. Single measurement expanded MU ranged from 2.8 % to 5.0 %. Expanded MU (k=2) for target value assignment ranged from 2.0 % to 3.4 % across the primary therapeutic range, reaching 7.1 % total error at the lower limit of the measuring interval (LLMI). CONCLUSIONS: This candidate RMP enables accurate determination of piperacillin in human serum and plasma, providing a standardized platform to facilitate reliable clinical TDM and routine assay harmonization.