Severe hospital-acquired pulmonary infections (sHAPi) can cause high hospital costs in critically ill patients and risks of mortality worldwide [1]. Data from the China Antimicrobial Surveillance Network showed that Pseudomonas aeruginosa (P. aeruginosa) represents one of the most frequent pathogens in the lower respiratory tract infection [2]. The prevalence of carbapenem-resistant P. aeruginosa (CRPA) and difficult-to-treat P. aeruginosa (DTR–P. aeruginosa) isolates were respectively reported to be 22.41% and 5.8% with an upward tendency, in China for the year of 2022 [2]. P. aeruginosa has an outstanding ability to rapidly develop further resistance to all first-line antibiotics and form an infectious biofilm to limit antimicrobial penetration, thus making pseudomonal infections more complicated and difficult to treat [3].

Ceftazidime/avibactam (CAZ/AVI), a novel compound preparation of β-lactam/β-lactamase inhibitor, has been approved for therapy of, for example, complicated intra-abdominal infections, hospital-acquired and ventilator-associated pneumonia, and complicated urinary tract infections [4]. CAZ/AVI has exhibited potent antibacterial activity against CRPA and DTR–P. aeruginosa isolates collected from 30 medical centres in China 2022 [2]. Unfortunately, studies on the effectiveness and safety of CAZ/AVI in clinical practice are limited. In fact, most of these studies have also been carried out in fairly small patient cohorts, especially data in terms of severe pulmonary infections and DTR–P. aeruginosa associated infections [5], [6], [7].

Besides the challenge of multidrug-resistant (MDR) bacteria with increased MIC, antibacterial treatment of sHAPi is also facing a wide range of difficulties. Despite optimal pharmacokinetic/pharmacodynamics (PK/PD) exposure against P. aeruginosa in the plasma, CAZ showed relatively poor penetration into epithelial lining fluid (ELF), even with intravenous continuous infusion [8]. Moreover, any pathophysiological changes (e.g., altered fluid status, renal or hepatic dysfunction, organ support, microvascular failure) in patients with sHAPi may have adverse influence on antibiotic concentrations in the infection sites and subsequent clinical outcomes [9]. It has been reported that CAZ/AVI therapy has poor outcomes among patients with pneumonia caused by carbapenem-resistant Enterobacteriaceae and those receiving renal replacement therapy [10].

Hence, this retrospective study aimed to expand and fortify the evidence base for the clinical efficacy of CAZ/AVI for the treatment of this life-threatening infection caused by CRPA or DTR–P. aeruginosa and offer new insights into the utility of CAZ/AVI in critically ill patients.