OBJECTIVES: Conduct a cost effectiveness analysis of ertapenem in the treatment of moderate community acquired intra-abdominal infections, from the Instituto Mexicano del Seguro Social (IMSS) perspective. METHODS: Cost-effectiveness analysis from the IMSS perspective based on a decision analytic model of hypothetical cohorts. Target population was patients over 15 years covered by IMSS with moderate community acquired intra-abdominal infection caused by E. coli