Bactericidal Activity, Absence of Serum Effect, and Time-Kill Kinetics of Ceftazidime-Avibactam against β-Lactamase-Producing Enterobacteriaceae and Pseudomonas aeruginosa

Avibactam, a non-beta-lactam beta-lactamase inhibitor with activity against extended-spectrum beta-lactamases (ESBLs), KPC, AmpC, and some OXA enzymes, extends the antibacterial activity of ceftazidime against most ceftazidime-resistant organisms producing these enzymes. In this study, the bactericidal activity of ceftazidime-avibactam against 18 Pseudomonas aeruginosa isolates and 15 Enterobacteriaceae isolates, including wild-type isolates and ESBL, KPC, and/or AmpC producers, was evaluated. Ceftazidime- avibactam MICs (0.016 to 32 mu g/ml) were lower than those for ceftazidime alone (0.06 to >= 256 mu g/ml) against all isolates except for 2 P. aeruginosa isolates (1 bla(VIM)-positive isolate and 1 bla(OXA)-23-positive isolate). The minimum bactericidal concentration/MIC ratios of ceftazidime-avibactam were <= 4 for all isolates, indicating bactericidal activity. Human serum and human serum albumin had a minimal effect on ceftazidime-avibactam MICs. Ceftazidime-avibactam time-kill kinetics were evaluated at low MIC multiples and showed time-dependent reductions in the number of CFU/ml from 0 to 6 h for all strains tested. A >= 3-log(10) decrease in the number of CFU/ml was observed at 6 h for all Enterobacteriaceae, and a 2-log(10) reduction in the number of CFU/ml was observed at 6 h for 3 of the 6 P. aeruginosa isolates. Regrowth was noted at 24 h for some of the isolates tested in time-kill assays. These data demonstrate the potent bactericidal activity of ceftazidime-avibactam and support the continued clinical development of ceftazidime-avibactam as a new treatment option for infections caused by Enterobacteriaceae and P. aeruginosa, including isolates resistant to ceftazidime by mechanisms dependent on avibactam-sensitive beta-lactamases.