Comparison of Dual Versus Additional Tigecycline in Colistin-Sulbactam Regimen for Treatment of Carbapenem-Resistant Acinetobacter baumannii Pneumonia

Background: Acinetobacter baumannii is a leading cause of hospital-acquired infections and is frequently drug-resistant. Although the 2024 IDSA guidance recommends sulbactam-durlobactam plus a carbapenem for CRAB pneumonia, this regimen is not widely available. As an alternative, colistin with high-dose sulbactam, with or without tigecycline, is often used. This study compared outcomes between dual therapy (colistin-sulbactam) and triple therapy including tigecycline. Materials and Methods: A retrospective cohort study was conducted at Phramongkutklao Hospital from 2019 to 2024. Medical records of patients diagnosed with CRAB pneumonia were reviewed and categorized into 2 treatment groups: the dual regimen group (colistin-sulbactam) and the triple regimen group (colistin-sulbactam-tigecycline). The primary outcome was 28-day all-cause mortality. Results: Fifty-one patients were included: 34 received dual regimen and 17 received triple regimen. Those in the triple regimen group had a significantly higher incidence of pneumonia-related complications, including septic shock (82.4% vs. 47.1%, P =0.016) and disseminated intravascular coagulation (76.5% vs. 29.4%, P =0.001). The 28-day mortality was numerically lower with triple therapy (35.3% vs. 41.2%), but this difference was not statistically significant ( P =0.717). Adverse events were comparable between groups, and tigecycline was generally well tolerated. Conclusions: Triple therapy with tigecycline showed no significant survival benefit over colistin-sulbactam in CRAB pneumonia, although a potential advantage cannot be excluded. Larger, adequately powered prospective studies are needed to clarify its role, particularly in regions where sulbactam-durlobactam is not yet available.