The 5 oral aminosalicylate preparations available for use in the United States are sulfasalazine (Azulfidine), mesalamine (Asacol, Asacol HD, Pentasa, Lialda, Apriso), balsalazide (Colazal), and olsalazine (Dipentum). Enema and suppository formulations are also available. All of these are derivatives of 5-aminosalicylic acid (5-ASA); the major differences are in the mechanism and site of delivery. Some of these agents also have unique adverse effects lacking in other agents of this class.

All of the aminosalicylates are useful for treating flares of IBD and for maintaining remission. None of the aminosalicylates has been proven to have greater efficacy than any of the others for the treatment of ulcerative colitis. As a class, these agents appear to be more effective in persons with ulcerative colitis than in persons with Crohn disease; in persons with mild Crohn disease, the primary utility is for colonic disease (as is the case with sulfasalazine^[3] ; administer folic acid if sulfasalazine is used). Aminosalicylates have only a weak effect in preventing recurrence after surgery in patients with Crohn disease.^[84]

For patients in remission from distal ulcerative colitis, oral or rectal 5-ASA can be used to manage this disease, as well as a combination regimen of oral and topical 5-ASA.^[3] In treating rectal disease, rectal 5-ASA is preferred over rectal steroids.^[3]A dose response has been described regarding the use of these agents for ulcerative colitis. For moderate disease, a dose of 4.8 g/day of mesalamine has been shown to be more efficacious than 2.4 g/day.^[85]

Types and Administrative Methods There are a number of 5-ASA medications which differ based on primary medication type, medication coating, or route of administration (oral vs. rectal). The first 5-ASA widely used in IBD was sulfasalazine (Azulfidine®). Sulfasalazine is still used, however, some patients experience side effects due to the sulfa component (see below). Another form of 5-ASA is known as mesalamine, which does not contain a sulfa group. Approximately 90% of those with intolerance to sulfasalazine can tolerate mesalamine. There are several mesalamine-based oral 5-ASA agents including, Asacol®HD, Pentasa®, Lialda®, Apriso™, Delzicol™. These agents all use the same mesalamine, but differ in terms of the medication coating. Mesalamine must be coated or placed in special capsules to ensure drug delivery to the intestine or colon. The difference in coating affects where the medication is released in the intestine or colon and how frequently the medication needs to be taken (once, twice, or three times daily). Other forms of 5-ASA used include olsalazine (Dipentum®) or balsalazide (Colazal™), which are also effective therapies for ulcerative colitis. In many situations, rectal therapies using 5-ASA agents can dramatically improve control of IBD. Rectal administration permits delivery of high dose therapy (targeted exactly where it is needed) and avoids systemic (body wide) exposure. In many cases, rectal therapies are used in conjunction with oral therapies for additional symptom improvement:

• Suppositories (Canasa®) deliver mesalamine directly to the rectum. A high proportion of patients with proctitis (inflammation in the rectum) will respond to mesalamine suppositories. These are usually given in single or twice-daily doses and can provide substantial relief from the urgency and frequency of bowel movements. A suppository is inserted into the rectum and does not need to be passed or removed. A combination of rectal and oral therapies may be more effective than pills alone. 

• Enema formulations (Rowasa®) allow mesalamine to be applied directly to the left colon, reaching higher than the suppository alone. Up to 80 percent of patients with left-sided colon inflammation benefit from using this therapy once a day. Enemas are liquid and should remain in the colon for at least 20-40 minutes.

Source: http://emedicine.medscape.com/article/179037-treatment#d11