Population pharmacokinetics of piperacillin/tazobactam in critically ill pediatric patients.

Piperacillin-tazobactam is commonly used in critically ill pediatric patients; however, standard dosing regimens may not reliably achieve maximally effective exposures in this population. To characterize the population pharmacokinetics of piperacillin-tazobactam in critically ill pediatric patients and evaluate the adequacy of commonly used dosing regimens, plasma concentrations were obtained around a single dose of piperacillin-tazobactam in critically ill pediatric patients aged 1 month to 12 years. A simultaneous population pharmacokinetic model for piperacillin and tazobactam was developed using nonlinear mixed-effects modeling. Monte Carlo simulations were performed to assess the probability of target attainment (PTA) for short, extended, and continuous infusion regimens across a range of ages and renal function states. Dosing adequacy was defined by simultaneous attainment of target drug exposures for piperacillin (100%fT > MIC) and tazobactam (85%fT > 2 mg/L). Thirty-one patients contributed 102 plasma samples, of which only 22.6% of patients achieved simultaneous piperacillin-tazobactam target exposures, considering a piperacillin MIC of 16 mg/L. Renal function and infusion duration were the primary determinants of attainment of target attainment. Standard short infusions frequently failed to achieve combined target exposures, particularly in patients with preserved renal function or augmented renal clearance (ARC). Extended infusions improved PTA, but remained suboptimal at higher MICs. Continuous infusion consistently achieved the highest target drug exposures across all simulated scenarios. Short intermittent piperacillin-tazobactam infusions and even extended infusions often result in suboptimal exposure in critically ill pediatric patients. Continuous infusion represents a rational dosing strategy to improve combined target attainment, particularly in children with preserved or ARC.