This dose comparison study, taking place at over 200 sites worldwide, will compare the dosing, safety and efficacy of an investigational medicine OPC-6535 to the dosing, safety and efficacy of Asacol ® in the maintenance of remission in subjects with ulcerative colitis.

Objective(s):

This study will compare the safety and efficacy of 25 mg per day (QD) and 50 mg QD of OPC-6535 to 800 mg twice a day (BID) of Asacol® in the maintenance of remission in subjects with ulcerative colitis.

Subject Population:

• Subjects with ulcerative colitis currently in remission defined as rectal bleeding (RB) and flexible sigmoidoscopy (FS) scores of 0, on or off a stable dose of sulfasalazine or 5-ASA products for at least 6 weeks.
• Subjects must have had the diagnosis of ulcerative colitis established by prior colonoscopy or undergo colonoscopy in lieu of flexible sigmoidoscopy during the Screening Period.
• Subjects must have had treatment for a flare of ulcerative colitis, with symptomatic onset of remission occurring no more than 52 weeks from the Screening Period.
• Subjects may not have used corticosteroids, topical agents (corticosteroid or 5-ASA enemas, suppositories, foams), azathioprine, 6-mercaptopurine, or methotrexate within 6 weeks of the Screening Period. Upon entry, sulfasalazine and 5-ASA containing products will be discontinued.

Safety: Vital signs, ECGs, laboratory studies (including hematology, clinical chemistry, and urinalysis), and adverse events.

Inclusion Criteria:

• Male or female subjects, 18 to 80 years of age, inclusive.
• Subjects with a prior diagnosis of ulcerative colitis, established by colonoscopy.
• Subjects currently in remission.
• Subjects who have undergone treatment for a flare of ulcerative colitis, with symptomatic onset of remission occurring no more than 52 weeks from the Screening Period.
• If subjects are taking sulfasalazine or 5-ASA products prior to entry, the dose must be stable for at least 6 weeks prior to the Screening Period. NOTE: During the study, use of these drugs will be discontinued.
• Subjects having undergone colonoscopy with pan-colonic surveillance biopsies negative for dysplasia within 1 year of the Screening Visit if at increased risk of colorectal cancer (≥ 8 year history of ulcerative colitis).
• Female or male subjects who are surgically sterilized or who are prepared to and agree to practice a double-barrier form of birth control from the Screening Period through 30 days (females) and 90 days (males), respectively, from the last dose of study medication. Females who are more than 12 months post-menopausal are also eligible to participate in the study.

Exclusion Criteria:

• Subjects who have active disease.
• Subjects who have any other clinically significant disease(s) or condition/procedure(s).
• Subjects who have had major gastrointestinal surgery including, but not limited to, a colostomy, an ileostomy or previous colonic surgery other than appendectomy.
• Subjects who have used corticosteroids or topical agents (corticosteroid or 5-ASA enemas, suppositories, foams) within 6 weeks of the Screening Period.
• Female subjects who are pregnant or lactating.
• Other exclusion criteria may apply.