In vitro activity of ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam alone or in combination with polymyxin B against carbapenem resistant Acinetobacter baumannii

Nosocomial infection caused by Carbapenem-Resistant Acinetobacter baumannii (CR-A. baumannii) has become a challenge in clinical practice. Acting as the last resort antibacterial agents for the treatment of CR-A. baumannii infection, polymyxins have high risk of nephrotoxicity and poor clinical efficacy. Ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam are three beta-lactam/beta-lactamase inhibitor combination complexes that newly approved by the Food and Drug Administration for the treatment of carbapenem-resistant Gram-negative bacterial infection. In this study, we analyzed the in vitro activity of those novel antibacterial agents alone or in combination with polymyxin B against the CR-A. baumannii obtained from a Chinese tertiary hospital. Our results suggest that those novel antibacterial agents should not be used alone for the treatment of CR-A. baumannii infection, as they cannot prevent the regrowth of bacteria at the clinical achievable blood concentration. Imipenem/relebactam and meropenem/vaborbactam should not be used as the substitutes of imipenem and meropenem for polymyxin B based combination therapy against CR-A. baumannii, since they have no edge over imipenem and meropenem on antibacterial activity when in combination with polymyxin B. Ceftazidime/avibactam may be more suitable than ceftazidime for polymyxin B based combination therapy against CR-A. baumannii, as it has a higher synergistic rate with polymyxin B, and the antibacterial activity of ceftazidime/avibactam is much higher than that of ceftazidime when tested in combination with polymyxin B. Ceftazidime/avibactam may also be the better choice than imipenem and meropenem for polymyxin B based combination therapy against CR-A. baumannii, as it has a higher synergistic rate with polymyxin B.