An Investigator-Blind, Randomized, Placebo-Controlled, Parallel-Group Study to Establish Therapeutic Equivalence of 1000 mg Mesalamine Rectal Suppositories and Canasa® Rectal Suppositories (1000 mg Mesalamine, USP) in the Treatment of Mild to Moderate Ulcerative Proctitis will be conducted in 533 patient with a estimated duration of 18months.