Efficacy & Safety of Infliximab Monotherapy Vs Combination Therapy Vs AZA Monotherapy in Ulcerative Colitis (Part 1) Maintenance Vs Intermittent Therapy for Maintaining Remission (Part 2)(Study P04807)

Part 1 of this study is a 3-arm, randomized, active-controlled, parallel-group, multicenter, double-blind, double-dummy, 16-week study to compare the efficacy and safety of infliximab (IFX), as monotherapy or in combination with azathioprine (AZA) versus AZA monotherapy in adults with moderate to severe active ulcerative colitis (UC). Participants who qualify at the Baseline Visit will be eligible to be randomized to one of the three active treatment groups. Participants in the IFX/AZA combination therapy and IFX monotherapy cohorts will receive IFX infusions at Weeks 0, 2, and 6 and daily oral AZA/placebo, respectively; participants in the AZA cohort will receive daily oral AZA and placebo infusions at Weeks 0, 2, and 6. At Week 8, all participants will be evaluated for response. Participants responding to IFX treatment at Week 8, either as monotherapy or in combination with AZA, will receive one more IFX infusion at Week 14; non-responders to IFX therapy will receive placebo infusions at Weeks 8 and 10 and one additional IFX infusion at Week 14. Participants responding to AZA monotherapy at Week 8 will continue on AZA therapy and receive one placebo infusion at Week 14; nonresponders to AZA will be eligible to receive IFX at Weeks 8, 10, and 14. Part 2: Participants in remission on IFX monotherapy or IFX/AZA treatment at Week 16 will be randomized to either maintenance or intermittent open-label IFX treatment; randomization will be stratified based on oral AZA/placebo treatment in Part 1. Oral AZA/placebo treatment will continue to be double-blinded. All participants will continue to receive oral AZA/ placebo for the duration of the study. Participants randomized to maintenance IFX treatment will receive scheduled IFX infusions every 8 weeks beginning at Week 22 (Week 6 for direct entry). If participants lose response, or if treatment has to be discontinued because of an adverse event, these participants are considered treatment failures, and should be follow