Critical threshold target attainment rates for tazobactam combined with piperacillin among patients admitted to the ICU with hospital-acquired pneumonia.

Optimizing antibiotic exposures in hospital-acquired pneumonia (HAP) is crucial; however, dosing decisions often overlook target levels for the beta-lactamase inhibitor tazobactam (TAZ), and the impact of renal dysfunction and renal replacement therapy on TAZ pharmacokinetics (PK) remains poorly described. We developed a population PK model of TAZ using 162 plasma samples from 35 ICU patients with HAP, including those receiving continuous renal replacement therapy (CRRT). TAZ concentrations were quantified using validated LC-MS/MS methods. A one-compartment model was fit using Monolix, with clearance modeled as a function of creatinine clearance, CRRT effluent flow rate, and intermittent hemodialysis. Monte Carlo simulations assessed the probability of unbound TAZ concentrations exceeding 1, 2, or 4 mg/L for 100% of the interval between 24 and 48 h across intermittent, extended, and continuous infusion (CI) regimens, stratified by renal function and CRRT. TAZ clearance was driven by renal function and CRRT flow rate. All regimens achieved ≥90% probability of target attainment (PTA) at thresholds of 1-2 mg/L. At 4 mg/L, PTA fell below 90% in patients with creatinine clearance ≥150 mL/min for all regimens, with low-dose CI performing the worst. High-dose CI improved PTA at this higher threshold but may increase the risk of piperacillin overexposure. TAZ exposures sufficient for enzymatic beta-lactamase inhibition are generally achieved with standard dosing for lower thresholds but not for more aggressive targets (e.g., high extended-spectrum β-lactamase expression), particularly in patients with preserved or augmented renal function, who may require therapeutic drug monitoring or alternative therapy.