A review.Metallo-β-lactamase enzymes, named because of the presence of one or two zinc ions at the catalytic site, are responsible for β-lactam antibiotic hydrolysis and are increasing in prevalence worldwide.Despite the increase in antibiotic development over the past decade, a β-lactamase inhibitor that binds to metallo- β-lactamases is not com. available.Treatment options for metallo-β-lactamases are restricted to non- β-lactam antibiotics, cefiderocol, or the combination of ceftazidime-avibactam and aztreonam.Aztreonam is stable against metallo-β-lactamase-mediated hydrolysis, and avibactam inhibits most other clin. relevant β-lactamase enzymes, making this an enticing combination.Aztreonam-avibactam requires two loading doses, administered sequentially over 30 min and then 3 h, with the maintenance regimen starting 3 h after the end of the second loading dose.Addnl., there might be some benefit with the addition of ceftazidime, as demonstrated in hollow-fiber infection models comparing ceftazidime-avibactam plus aztreonam with aztreonam-avibactam against regrowth of New Delhi metallo-β-lactamase 1-producing Enterobacteriaceae.Ultimately, the small number of patients with metallo- β-lactamases in the study restricts the ability to draw conclusions about the utility of aztreonam-avibactam in eradicating these difficult-to-treat pathogens.However, years of experience with the combination of ceftazidime-avibactam plus aztreonam suggest this combination reduces 30-day mortality compared with colistin-based regimens in patients with carbapenemresistant Enterobacterales infections.Importantly, the data evaluating ceftazidime-avibactam plus aztreonam are all observational in nature, and dosing is not standardised across studies.