Simultaneous determination of piperacillin, metronidazole, and tazobactam in plasma by UPLC–MS/MS and application to a pharmacokinetic study in pediatric liver transplant patients

Piperacillin/tazobactam and metronidazole are two commonly antimicrobials used to prevent and treat infections after liver transplantation in pediatric patients. However, under the recommended dose, it may lead to insufficient antimicrobial treatment and poor efficacy. To achieve antimicrobial therapy based on pharmacokinetic strategies, a rapid and highly sensitive ultra-high performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed to measure the plasma concentrations of piperacillin, tazobactam, and metronidazole in pediatric liver transplant recipients. Sample separation was achieved using an Acquity UPLC CSH C 18 column (2.1 × 50 mm, 1.7 μm) with gradient elution. The mobile phase consisted of ammonia solution–formic acid–water (0.5:1:1000, v / v /v) and methanol–acetonitrile (1:1, v/v). The plasma concentration range was 0.20–100.00 μg/mL, with good linear range. The intra- and inter-day precisions were less than 13.4 %, and the accuracy ranged from 90.0 % to 109.0 %. The selectivity, carryover, dilution integrity, matrix effect, recovery, and stability met the requirements of the relevant guidelines. The established UPLC–MS/MS method was successfully applied to measure the concentrations of piperacillin, tazobactam, and metronidazole in the plasma of pediatric liver transplant patients. The results showed that according to the recommended dosing regimen, piperacillin/tazobactam reached the effective therapeutic target of 50 %T > MIC in only 4 h. The maximum plasma concentration (C max ) of metronidazole ranged from 9.46 to 28 μg/mL, with an average C max of 16.59 μg/mL, which did not achieve the ideal C max /MIC ratio of 8–10.