Medical uses
Crohns disease
Three phenotypes, or categories of disease, are present in Crohns disease: stricturing disease (which causes narrowing of the bowel), penetrating disease (which causes fistulae or abnormal connections of the bowel), and inflammatory disease (which primarily causes inflammation). Fistulizing disease
Infliximab was first used for closure of fistulae in Crohns disease in 1999. In a 94-patient, phase II clinical trial, the researchers showed Infliximab was effective in closing fistulae between the skin and bowel in 56-68% of patients. A large, 296-patient Phase III clinical trial called the ACCENT 2 trial showed infliximab was additionally beneficial in maintaining closure of fistulae, with almost two-thirds of all patients treated with the three initial doses of infliximab having a fistula response after 14 weeks, and 36% of patients maintaining closure of fistulae after a year, compared with 19% who received placebo therapy. This final trial resulted in the FDA approval of the drug to treat fistulizing disease. Inflammatory disease
Infliximab has been used to induce and maintain remission in inflammatory Crohns disease. The ACCENT 1 trial,  a large, multicentre trial, found 39 to 45% of patients treated with infliximab, who had an initial response to it, maintained remission after 30 weeks, compared with 21% who received placebo treatment. It also showed a mean maintenance of remission from 38 to 54 weeks compared with 21 weeks for patients who received placebo treatment.Crohns patients have flares of their disease between periods of disease quiescence.
Some of the most severe are:

serious infections
reactivation of hepatitis B
reactivation of tuberculosis
lethal hepatosplenic T-cell lymphoma (generally only when combined with 6-mercaptopurine)
drug-induced lupus
demyelinating central nervous system disorders
psoriasis and psoriasiform skin lesions
new-onset vitiligoCases of leukopenia, neutropenia, thrombocytopenia, and pancytopenia (some fatal) have been reported with infliximab. The FDA issued a warning to doctors appearing in the respective product labeling of infliximab instructing them to screen and monitor potential patients more carefully. The FDA issued a warning to doctors that there is an increased risk of lymphoma and other cancers associated with the use of infliximab and other tumor necrosis factor blockers in children and adolescents.Maintenance therapy with the drug (versus intermittent or sporadic therapy) lessens the likelihood of developing antibodies to infliximab which are known to reduce the efficacy of the drug. Combination treatment with methotrexate (an antifolate drug which suppresses the immune system) has been shown to reduce the formation of these antibodies in patients with rheumatoid arthritis and combination therapy with other immunosuppressants has been shown to reduce the likelihood of these antibodies being formed in Crohns disease. The use of immunosuppressants may not be necessary in all diseases for which infliximab is indicated, and indiscriminant uses of these other immunosuppressants carry their own risks. Infliximab was studied in monotherapy (without concomitant immunosuppressants such as methotrexate or azathioprine) in psoriasis, psoriatic arthritis, and ankylosing spondylitis.