Defining the pharmacokinetic/pharmacodynamic index of piperacillin/tazobactam within a hollow-fibre infection model to determine target attainment in intensive care patients

Background It is important to optimize dosing schemes of antibiotics to maximize the probability of therapeutic success. The recommended pharmacokinetic/pharmacodynamic (PK/PD) index for piperacillin/tazobactam therapy in clinical studies ranges widely (50%–100% fT>1–4×MIC). Dosing schemes failing to achieve PK/PD targets may lead to negative treatment outcomes. Objectives The first aim of this study was to define the optimal PK/PD index of piperacillin/tazobactam with a hollow-fibre infection model (HFIM). The second aim was to predict whether these PK/PD targets are currently achieved in critically ill patients through PK/PD model simulation. Patients and methods A dose-fractionation study comprising 21 HFIM experiments was performed against a range of Gram-negative bacterial pathogens, doses and infusion times. Clinical data and dose histories from a case series of nine patients with a known bacterial infection treated with piperacillin/tazobactam in the ICU were collected. The PK/PD index and predicted plasma concentrations and therefore target attainment of the patients were simulated using R version 4.2.1. Results fT >MIC was found to be the best-fitting PK/PD index for piperacillin/tazobactam. Bactericidal activity with 2 log10 cfu reduction was associated with 77% fT>MIC. Piperacillin/tazobactam therapy was defined as clinically ‘ineffective’ in ∼78% (7/9) patients. Around seventy-one percent (5/7) of these patients had a probability of >10% that 2 log10 cfu reduction was not attained. Conclusions Our dose-fractionation study indicates an optimal PK/PD target in piperacillin/tazobactam therapies should be 77% fT>MIC for 2 log10 kill. Doses to achieve this target should be considered when treating patients in ICU.