To establish non-inferiority of the use of the therapy with ertapenem between three days versus 7 days of treatment, was considered a significance level of 5%, 95% confidence interval, a power of 80% and in the group control of 60%, a margin of not less 10% is considered of no clinical importance. For a balanced design of type n1 = n2 r = 1. Still needed 26 patients per group. The period of advance recruitment of patients was 6 months.