The primary pharmacology of ceftazidime/avibactam: resistancein vitro

This article reviews resistance to ceftazidime/avibactam as an aspect of its primary pharmacology, linked thematically with recent reviews of the basic in vitro and in vivo translational biology of the combination (J Antimicrob Chemother 2022; 77: 2321-40 and 2341-52). In Enterobacterales or Pseudomonas aeruginosa, single-step exposures to 8× MIC of ceftazidime/avibactam yielded frequencies of resistance from <∼0.5 × 10-9 to 2-8 × 10-9, depending on the host strain and the β-lactamase harboured. β-Lactamase structural gene mutations mostly affected the avibactam binding site through changes in the Ω-loop: e.g. Asp179Tyr (D179Y) in KPC-2. Other mutations included ones proposed to reduce the permeability to ceftazidime and/or avibactam through changes in outer membrane structure, up-regulated efflux, or both. The existence, or otherwise, of cross-resistance between ceftazidime/avibactam and other antibacterial agents was also reviewed as a key element of the preclinical primary pharmacology of the new agent. Cross-resistance between ceftazidime/avibactam and other β-lactam-based antibacterial agents was caused by MBLs. Mechanism-based cross-resistance was not observed between ceftazidime/avibactam and fluoroquinolones, aminoglycosides or colistin. A low level of general co-resistance to ceftazidime/avibactam was observed in MDR Enterobacterales and P. aeruginosa. For example, among 2821 MDR Klebsiella spp., 3.4% were resistant to ceftazidime/avibactam, in contrast to 0.07% of 8177 non-MDR isolates. Much of this was caused by possession of MBLs. Among 1151 MDR, XDR and pandrug-resistant isolates of P. aeruginosa from the USA, 11.1% were resistant to ceftazidime/avibactam, in contrast to 3.0% of 7452 unselected isolates. In this case, the decreased proportion susceptible was not due to MBLs.