 This is a randomized the study medication is assigned by chance, double-blind neither physician nor patient knows the treatment that the patient receives, active-controlled agent that is compared with a study medication to test whether the study medication has a real effect in a clinical study, double-dummy placebo inactive substance that is compared with a medication to test whether the medication has a real effect in a clinical study is administered to maintain the blind when the comparator medication cannot be made identical to the study medication, parallel-group each group of patients will be treated at the same time, multicenter study to assess the effectiveness and safety of 7 day course of doripenem, compared with 10 day course of imipenem-cilastatin in patients with ventilator-associated pneumonia. This study will consists of 3 phases: 1 a pretreatment phase with a maximum of 24 hours for the screeningbaseline visit, 2 a double blind, double dummy, treatment phase of 10 days Day 1 to Day 10 and an end-of-treatment EOT assessment within 24 hours after the last dose of study medication therapy administered on Day 10 or at the time of early withdrawal from study medication, and 3 a post treatment follow-up phase consisting of an early follow-up EFU visit within 7 to 14 days after the last dose of study medication, and last follow-up LFU visit within 28 to 35 days after the last dose of study medication for all patients including those who discontinued study medication early. Two hundred and seventy four patients will be randomly assigned to receive either doripenem or imipenem with placebo of the other medication given simultaneously to maintain the blind eg, 1 group will receive blinded doripenem from Days 1 to 7 and imipenem placebo Days 1 to 10, other group will receive blinded imipenem Days 1 to 10 and doripenem placebo Days 1 to 7. A sample of secretions from the lower respiratory tract will be obtained by bronchoalveolar lavage BAL or mini-BAL within 36 hours prior to administration of study medication from the enrolled patients and sent for culture. Patients, whose baseline BAL or mini-BAL culture results will yield at least 1 qualifying pneumonia pathogen will continue to receive study medication therapy and patients, whose baseline BAL or mini-BAL culture results did not yield at least 1 qualifying pneumonia pathogen will be discontinued from study medication therapy but will remain enroll in the study and will be followed for safety. Safety evaluations including adverse events, clinical laboratory evaluations, vital signs and physical examinations will be monitored throughout the study period. The total duration of an individual patients participation in the study will be approximately 5 to 6 weeks. 