Steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam administered by prolonged infusion in hospitalised patients

The objective of this study was to evaluate the steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam, administered by prolonged infusion, in hospitalised patients requiring antimicrobial therapy. Thirteen patients received 4.5g every 8h (q8h), infused over 4h, and pharmacokinetic parameters were determined by non-compartmental methods. Monte Carlo simulations (10 000 patients) were performed to calculate the cumulative fraction of response (CFR) for seven Gram-negative pathogens using minimum inhibitory concentration (MIC) data from the Meropenem Yearly Susceptibility Test Information Collection (2004–2007, USA) as well as the probability of target attainment (PTA) at MICs ranging from 1μg/mL to 64μg/mL. The pharmacodynamic target was free piperacillin concentration remaining above the MIC for 50% of the dosing interval. Mean±standard deviation maximum and minimum serum concentrations, half-life, volume of distribution at steady-state and systemic clearance of piperacillin were 108.2±31.7μg/mL, 27.6±26.3μg/mL, 2.1±1.2h, 22.1±4.0L and 8.6±3.0L/h, respectively. The CFR was >90% for Escherichia coli, Serratia marcescens and Citrobacter spp., 88.6% for Enterobacter spp., 87% for Klebsiella pneumoniae, 85.5% for Pseudomonas aeruginosa and 52.8% for Acinetobacter spp. The PTA was 100%, 81.1% and 12.3% at MICs of ≤16μg/mL, 32μg/mL and 64μg/mL, respectively. Piperacillin/tazobactam 4.5g q8h infused over 4h provides excellent target attainment for bacterial pathogens with MICs≤16μg/mL. However, the CFR was <90% for four of the seven Gram-negative pathogens evaluated.