The purpose of this study is to compare the microbiological cure rate of doripenem versus a comparator antibiotic in the treatment of patients with complicated urinary tract infection or pyelonephritis. The study will also characterize the safety and tolerability of treatment with doripenem in patients with complicated urinary tract infection or pyelonephritis.

Doripenem is an antibiotic medication not yet approved by the US FDA. This is a phase 3, multi-center, randomized, prospective, double-blind study of doripenem versus comparator in the treatment of complicated lower urinary tract infections (UTI) or pyelonephritis in adults. After the screening, patients are randomized to receive either doripenem or comparator. Patients are hospitalized, but subsequently, patients may be treated as outpatient or through home-based therapy at the investigators' discretion. Conventional laboratory data are collected from all patients at specified times throughout the study. The primary endpoint is microbiological response measured at test of cure visit. The patients receive either doripenum or comparator; duration of therapy is 10 days.

Inclusion Criteria:

• Diagnosis of complicated lower urinary tract infection or pyelonephritis

Exclusion Criteria:

• Women who are pregnant, nursing or of child-bearing potential and not using a medically accepted, effective method of birth control
• History of moderate or severe hypersensitivity reactions to antibiotic medications