This is a randomized (study drug assigned by chance), open-label (all people involved know the identity of the intervention), multicenter study that will evaluate the safety and tolerability of doripenem (an antibiotic used to treat infections) in patients with ventilator-associated pneumonia (VAP) or complicated intra-abdominal infection (cIAI). Approximately 250 patients will be assigned in a 3:1 ratio to receive doripenem or imipenem/cilastatin (188 patients randomized to receive doripenem and 62 patients randomized to receive imipenem/cilastatin). Furthermore, patients who receive doripenem or imipenem/cilastatin will be stratified by disease (VAP or cIAI). Therefore, for reporting purposes, there will be 4 groups: Patients with VAP treated with doripenem, patients with VAP treated with imipenem/cilastatin, patients with cIAI treated with doripenem, and patients with cIAI treated with imipenem/cilastatin. Study drug will be administered intravenously (iv) (through a vein) for 7 to 14 days for patients with VAP and for 5 to 14 days for patients with cIAI. The maximum duration of study drug is 14 days. Vancomycin and/or amikacin may be added to the study drug regimen as adjunctive therapy for those patients who meet study specified criteria. The recommended dosage of vancomycin is 1 g every 12 hours administered by iv infusion. The addition of amikacin is at the discretion of the investigator for patients with VAP (not cIAI) and the recommended dosing regimen for amikacin is 15 mg/kg given iv once a day. Alternative amikacin regimens or other aminoglycoside regimens may be permitted. Safety will be assessed during the study by the monitoring of adverse events, evaluation of laboratory test results, and changes in vital signs. The primary endpoint of this study is to assess the overall incidence of treatment-emergent adverse events (TEAEs) from the initiation of the first infusion of study drug and up to 30 days after the completion of study drug therapy. Treatment-emergent adverse events are defined as adverse events that occur or worsen between the initial infusion of study drug up to 30 days after the last dose of study drug. The hypothesis for this study is that doripenem has a similar safety profile to imipenem. Doripenem (1g at 8-hour intervals over a period of 4 hours) or imipenem/cilastatin (1g at 8-hours over a period of 1 hour) will be administered by intravenous (iv) infusion (delivery of drug slowly into the vein over a period of time). Patients diagnosed with ventilator associated pneumonia (VAP) will be treated for 7 to 14 days and patients with complicated intra-abdominal infections (cIAI) will be treated for 5 to 14 days.