OBJECTIVES: To compare Ertapenem with piperacillin/tazobactam (pip/tazo) for the treatment of moderate to severe community acquired intra-abdominal infections (c-IAI) in Colombia healthcare setting, with respect to cost and outcomes taking into account development of anti-microbial resistance (AMR). METHODS: A previously published decision tree model was adapted to estimate cost-effectiveness of Ertapenem vs. pip/tazo. Clinical efficacy, adverse events and medical resource use were derived from literature. AMR to Ertapenem and pip/tazo was calculated as weighted average based on the % distribution of different pathogens in c-IAI in Colombia and the sensitivity of Erta vs. pip/tazo for each pathogen from Colombia SMART data. The resistance-adjusted effectiveness is then computed based on efficacy from clinical trial and local AMR data, Model outcomes included resistance, clinical success, deaths, life years, direct costs, and costs per successfully treated patient. RESULTS: The overall resistance of Ertapenem vs. pip/tazo for c-IAI is 21.4% vs. 43.4%. The resistance-adjusted effectiveness are 70.3% vs. 46% for Ertapenem vs. pip/tazo. Daily drug costs are 133,550 (Ertapenem) vs. 34,989 (pip/tazo) Colombian Pesos. Total costs (including drug costs, hospitalization, cost of 2^nd-line treatment & cost of AEs) are 7,162,081 (Ertapenem) vs. 7,230,902 (pip/tazo) Pesos. During the first hospitalization period, Ertapenem is associated with a 24.3% higher treatment success rate, and a 68,821 Pesos in cost saving when compared with Pip/tazo. The Incremental cost per successfully treated patient (ICER) is -283,405 Colombian Pesos ($145.39 USD) for Ertapenem vs. Pip/tazo. CONCLUSIONS: Accounting for local anti-microbial resistance, Ertapenem is more effective and cost-saving vs. pip/tazo for the treatment of moderate to severe community acquired intra-abdominal infections in Colombia.