On the basis of monotherapy for intra-abdominal infection, the investigators are conducting this study to identify the difference of drug efficacy between ampicillin/sulbactam and moxifloxacin.

Inclusion Criteria:

• patients diagnosed of complicated intra-abdominal infection need surgical treatment

Exclusion Criteria:

• patients diagnosed of intra-abdominal infection receive non-operative management
• patients with known allergic history of fluoroquinolone
• Severe, life threatening disease with a life expectancy of < 48 h or APS and APACHE scores of > 35