The polymicrobial nature of complicated intra-abdominal infections makes these infections particularly challenging to treat. The initial selection of antimicrobial therapy is therefore extremely important. Inappropriate empiric antimicrobial therapy has been shown to delay clinical resolution, increase length of hospital stay, and increase the risk of mortality. In addition, the increasing frequency with which resistant isolates (e.g., extended spectrum beta-lactamases [ESBLs]) are recovered from patients mandates that empiric antimicrobial therapy covers these difficult-to-treat organisms. Here, we assessed the efficacy of a new antimicrobial agent, tigecycline. This is a combined analysis of data from the European sites that participated in two Phase III, double-blind trials to evaluate the efficacy and safety of tigecycline, versus that of imipenem/cilastatin, in adults with complicated intra-abdominal infections. Patients received either tigecycline (initial dose of 100 mg, followed by 50 mg intravenously every 12 hours) or imipenem/cilastatin (500/500 mg intravenously every 6 hours) for 5-14 days. The primary end point was the clinical response at the test-of-cure visit (12-44 days after therapy) in the co-primary microbiologically evaluable (ME) and microbiological modified intent-to-treat (m-mITT) populations. For the ME group, clinical cure rates at the test-of-cure visit were 92.4% (219/237) for tigecycline versus 88.8% (198/223) for imipenem/cilastatin (95% CI = -2.2, 9.4). Clinical cure rates for the mmITT populations were 87.3% (247/283) for tigecycline versus 83.5% (228/273) for imipenem/cilastatin (95% CI = -2.5, 10.0) at the test-of-cure visit. Pretherapy in vitro activity against baseline isolates for tigecycline and imipenem/cilastatin were also determined. The mean MIC(90) for tigecycline against the most commonly isolated aerobes and anaerobes was < or =2.0 microg/mL. No pretherapy isolates displayed resistance to tigecycline based on the breakpoints used. Bacterial susceptibilities to tigecycline appeared to be consistent with clinical responses. Most commonly reported treatment emergent adverse events for tigecycline and imipenem/cilastatin were nausea (14.7% and 11.8%, respectively, p = 0.267) and vomiting (10.7% and 7.3%, respectively p = 0.146). This combined analysis demonstrates that tigecycline is safe and effective for the treatment of complicated intra-abdominal infections, and reflects the findings of the global population.