Comparison of ceftazidime-avibactam and ceftolozane-tazobactam in vitro activities when tested against gram-negative bacteria isolated from patients hospitalized with pneumonia in United States medical centers (2017-2018).

Clinical isolates were consecutively collected from 70 United States medical centers in 2017-2018 and susceptibility tested by reference broth microdilution methods at a central laboratory. The most active agents against Enterobacterales (n = 3269) were ceftazidime-avibactam (99.9% susceptible), amikacin (98.7% susceptible), meropenem (97.4% susceptible), and tigecycline (94.6% susceptible), but only ceftazidime-avibactam and tigecycline retained good activity (≥90% susceptible) against carbapenem-resistant Enterobacterales (97.5% and 92.4% susceptible, respectively). The most active agents against multidrug-resistant (MDR) Enterobacterales were ceftazidime-avibactam (99.2% susceptible) and amikacin (90.9% susceptible), whereas ceftolozane-tazobactam and meropenem were active against only 53.8% and 78.1% of these organisms, respectively. Among ESBL-producing Enterobacterales (excluding carbapenemase-producing), susceptibility rates for ceftazidime-avibactam, ceftolozane-tazobactam, and meropenem were 100.0%, 84.1%, and 98.9%, respectively. Ceftazidime-avibactam and ceftolozane-tazobactam were very active against P. aeruginosa (n = 2215) and exhibited similar susceptibility rates (96.0% and 95.9% susceptible, respectively), including against meropenem-nonsusceptible (87.2% and 87.3% susceptible, respectively) and MDR (83.5% and 83.7% susceptible, respectively) isolates.