Study Comparing Cyclosporine With Infliximab in Steroid-refractory Severe Attacks of Ulcerative Colitis

Inclusion Criteria: * Age \> 18 years. * Diagnosis of UC according to Lennard-Jones criteria (Appendix 1). * Endoscopically demonstrated colorectal lesions localized above the anal margin and extending at least up to 15cm proximally. * Severe acute flare of UC with a Lichtiger Index score \> 10. * Refractoriness to high dose intravenous steroid therapy (≥ 0.8 mg/kg/d of methylprednisolone or equivalent) given for at least 5 days. * Adequate contraception for male or female subjects of childbearing potential, which will be continued throughout the study and at least 3 months after study termination. Exclusion Criteria: * Pregnant or breast-feeding woman. * Previous treatment with cyclosporine or infliximab. * Azathioprine or 6-mercaptopurine treatment initiated more than 4 weeks before inclusion. * Indication for immediate surgery. * History of colorectal dysplasia. * Diagnosis of Crohn's disease. * Positive stool tests for amoebiasis and/or positive bacteriological culture for Salmonella, Shigella, Yersinia and Campylobacter and/or presence of Clostridium difficile B toxin in the stools. * Renal failure (creatininemia \> upper limit of normal laboratory value). * Uncontrolled high blood pressure. * HIV, HBV viral infection (except the presence of positive anti-HBs antibodies) with serology not older than 3 months. * Uncontrolled bacterial or active viral infection. * Past medical history of malignant condition in the last 5 years (including leukaemia, lymphoma and myelodysplasia) except for baso-cellular cutaneous cancers. * Past medical history of myocardial infarction or heart failure. * Intradermal reaction to Tuberculin (Tubertest® 5 units) \> 5mm. * Active tuberculosis * Untreated latent tuberculosis (see national recommendations. Appendix 2). * Abnormal blood count with polynuclear neutrophils \< 1,500 G/L or white cells \< 3,000, or platelets \< 100,000 G/L. * Unexplained rise higher than 3 times the normal level for transaminases, alkaline phosphatases and/or higher than twice the normal level for bilirubin. * Non-compliant subjects. * Participation in another therapeutic study.