BACKGROUND: Ceftolozane/tazobactam (TOL/TAZ) and ceftazidime-avibactam (CAZ/AVI) are increasingly used to treat pneumonia caused by multidrug-resistant Gram-negative bacilli. However, data on intrapulmonary penetration to confirm dosing adequacy are limited. Therefore, the aim of this study was to compare epithelial lining fluid (ELF) penetration and pharmacokinetic/pharmacodynamic (PK/PD) target attainment of TOL/TAZ versus CAZ/AVI administered by continuous infusion (CI) in critically ill patients with nosocomial pneumonia. METHODS: . Simulations were performed to estimate the probability of attaining predefined joint ELF PK/PD target defined as free concentration 100% fT> minimum inhibitory concentration (MIC) for the β-lactam component and 100% fT> concentration threshold (CT) for the β-lactamase inhibitors, among relevant MIC scenarios. Three different dosing regimens (low, standard and high) were evaluated for each combination. RESULTS: 2 mg/L) at least the standard-dose regimen was required. More aggressive target scenarios reduced the probability of target attainment, particularly for inhibitor thresholds of 4 mg/L and for Enterobacterales-oriented joint targets. CONCLUSIONS: In critically ill adults with nosocomial pneumonia receiving TOL/TAZ or CAZ/AVI by CI, standard doses achieved ELF exposures consistent with dual PK/PD target attainment against all susceptible isolates. Interindividual variability and the risk of plasma overexposure support individualized dosing and consideration of therapeutic drug monitoring. TRIAL REGISTRATION: The trial was registered in the European Union Drug Regulating Authorities Clinical Trials Database (EudraCT No. 2021-006908-32). Registered 10 February 2022; https://www.clinicaltrialsregister.eu/ctr-search/trial/2021-006908-32/ES.
Benítez-Cano et al. (2026) studied this question.