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 vs non-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