Crohns disease is characterized by inflammation (the changes that happen when tissues in the body are injured) and ulceration (open sores) of the intestines. Crohns disease is treated with medications that decrease inflammation, and reduce diarrhea, abdominal pain and other symptoms of Crohns disease. In addition, Crohns disease can be treated with medications that suppress the immune system (the body system involved in inflammation and infections) or with surgery. This study will investigate the effectiveness of infliximab and azathioprine in the treatment of patients with moderate-to-severe Crohns disease. Infliximab is currently approved by the FDA for the treatment of both Crohns disease and rheumatoid arthritis. Azathioprine, which is an investigational drug, has not been approved by the FDA for the treatment of Crohns disease, but it is a well-established therapy that has been used for many years to treat Crohns disease. This study seeks to determine whether infliximab, azathioprine, or the combination of both drugs would be the most appropriate treatment for Crohns disease patients who have not responded well to certain drugs called 5-ASA drugs (e.g. Asacol, Pentasa, sulfasalazine) and/or require frequent treatment with corticosteroids. This research study will involve approximately 500 patients. Patients may participate in the main study for up to 34 weeks (approximately 8 months). During the main study, patients will be asked to visit the study center for 10 visits. If patients enroll into the extension of the study, the total time for participation may be up to 54 weeks (approximately 13 months). Patients enrolled in the Study Extension will be asked to visit the study center for an additional 5 visits. A country-specific (EU and Israel only), prospective, multi-center, open-label extension of the study will further evaluate the long-term safety and efficacy of scheduled maintenance therapy with infliximab in patients with Crohns Disease. Patients who have completed treatment through Week 50 in the SONIC main study and who, in the opinion of the investigator, would benefit from infliximab treatment may enter the open-label extension. Patients will be randomly assigned to one of three treatment groups (either infliximab plus placebo capsules, infliximab plus azathioprine, or azathioprine plus placebo infusions - there is no possibility of being assigned to placebo only in this trial - patients will receive one or both of these medications) at the beginning of the study. Oral medication will be taken daily. There are 5 infusion (which will be either infliximab or placebo) visits during the main study.
