Comparative effectiveness and safety of colistin-based versus high-dose ampicillin/sulbactam-based combination therapy for nosocomial pneumonia caused by carbapenem-resistant <i>Acinetobacter baumannii</i>

Differences exist between Infectious Diseases Society of America guidance and European Society of Clinical Microbiology and Infectious Diseases guidelines on treating pneumonia caused by carbapenem-resistant <i>Acinetobacter baumannii</i> (CRAB). This study compared the outcomes of colistin-based and high-dose ampicillin/sulbactam-based combination therapies in patients with CRAB nosocomial pneumonia. A retrospective cohort study was conducted at a university-affiliated hospital in South Korea. Patients received either a colistin-based regimen with a loading dose followed by a maintenance dose (June 2021-May 2022) or a high-dose ampicillin/sulbactam-based regimen with sulbactam 9 g/day (October 2022-September 2023). The primary outcome was 28-day all-cause mortality; secondary outcomes included 14-day/28-day clinical success rates and 14-day/28-day kidney injury based on the Risk, Injury, Failure, Loss, End-stage renal disease score. Logistic and Poisson regression analyses were used to compare outcomes between groups. Among 179 patients enrolled in the study, 84 received the colistin-based regimen and 95 received the high-dose ampicillin/sulbactam-based regimen. The ampicillin/sulbactam group showed significantly lower 28-day mortality (20% vs. 61%; adjusted relative risk [aRR] = 0.16, 95% CI 0.08-0.32). Clinical success rates were higher in the ampicillin/sulbactam group at both 14 days (39% vs. 23%; aRR = 2.19, 95% CI 1.10-4.37) and 28 days (55% vs. 32%; aRR = 2.71, 95% CI 1.14-5.20). Additionally, 28-day kidney injury was lower in the ampicillin/sulbactam group (0.63 ± 1.16 vs. 1.06 ± 1.35; aRR = 0.56, 95% CI 0.40-0.79). High-dose ampicillin/sulbactam-based combination therapy demonstrates superior outcomes over colistin-based combination therapy for CRAB nosocomial pneumonia, including lower mortality, higher clinical success rates, and reduced kidney injury.