Comparative effectiveness of ertapenem versus other empirical antibiotics in elderly patients with complicated intra-abdominal infection: a real-world inverse probability of treatment weighting study.

Background: Elderly adults with complicated intra-abdominal infection (cIAI) represent a functionally immunocompromised population due to immunosenescence, multimorbidity, and frailty. Optimizing empirical antibiotic therapy in this group is essential to improve outcomes while minimizing unnecessary broad-spectrum antimicrobial exposure and antimicrobial resistance (AMR) selection pressure. Ertapenem is a once-daily carbapenem with favorable pharmacological properties, yet contemporary real-world comparative data in older adults are limited. Methods: We conducted a retrospective, real-world comparative-effectiveness study of hospitalized adults aged ≥65 years with cIAI at a tertiary academic medical center from 2019 to 2025. Eligible patients received empirical monotherapy with ertapenem, meropenem, cefoperazone-sulbactam, or moxifloxacin for ≥72 hours. A multinomial propensity score-based inverse probability of treatment weighting (IPTW) approach was used to balance baseline covariates across the four regimens. The primary outcome was clinical cure or improvement. Secondary outcomes included all-cause in-hospital mortality, infection-related mortality, intra-abdominal infection-related mortality, duration of antibiotic treatment, and length of hospitalization. Prespecified subgroup analyses were conducted by age group (65-70, 71-80, ≥81 years) and infection source (gastrointestinal Results: A total of 609 patients met eligibility criteria: 129 received ertapenem, 135 meropenem, 125 cefoperazone-sulbactam, and 220 moxifloxacin. IPTW achieved excellent covariate balance, with all standardized mean differences <0.10. In IPTW-adjusted analyses, clinical cure or improvement did not differ significantly between ertapenem and comparator regimens, with adjusted risk differences ranging from 1.80% to 6.44% (all 95% confidence intervals including zero). Mortality outcomes were likewise comparable across groups. Subgroup analyses suggested that ertapenem was associated with higher cure rates and lower mortality in patients aged 65-70 years and those with non-gastrointestinal infection sources, although confidence intervals were wide, and these findings should be interpreted as exploratory. Differences in secondary outcomes varied across regimens. Conclusion: In this IPTW-adjusted real-world analysis of elderly adults with cIAI, ertapenem demonstrated clinical effectiveness comparable to meropenem, cefoperazone-sulbactam, and moxifloxacin. Given its once-daily dosing convenience and narrower ecological impact, ertapenem may represent a reasonable and stewardship-aligned empirical option for selected older patients. Prospective and multicenter studies incorporating microbiological and illness severity data are needed to validate these findings.