Drug Therapy of Inflammatory Bowel Disease

Although the etiology of inflammatory bowel disease is unknown and specific therapy is unavailable, enough information on existing empiric agents is available to allow rational therapy. These agents include sulfasalazine, steroids, immunosuppressive drugs, metronidazole and cholestyramine. Sulfasalazine is a two-part molecule that depends on bacterial cleavage in the colon to deliver locally acting 5-aminosalicylate, whose mechanism of action may relate to inhibition of prostaglandin synthesis. The other half of the molecule, sulfapyridine, is responsible for most of the side effects of the drug. While the efficacy of sulfasalazine in the treatment and prevention of attacks of ulcerative colitis is well established, its use in Crohn's disease appears to be limited to patients with active colitis and ileo-colitis. Sulfasalazine is of major benefit in preventing relapses in patients with ulcerative colitis in remission. New formulations of 5-aminosalicylate may allow delivery of the apparently active moiety to the small bowel and colon without concomitant sulfapyridine toxicity. Corticosteroids are highly effective in acute attacks of ulcerative colitis and Crohn's ileitis and ileo-colitis; the mechanism of antiinflammatory action remains speculative. However, maintenance therapy with steroids is ineffective in preventing relapses or recurrent attacks of either ulcerative colitis or Crohn's disease. Steroid enemas allow topical administration to patients with distal colitis and proctitis with few systemic side effects. In children with growth failure associated with active Crohn's disease, amelioration by steroid therapy may actually restore normal growth. Immunosuppressive agents such as azathioprine and 6-mercaptopurine are of little value in active Crohn's disease when administered alone; however, in combination with other agents they may help diminish steroid dose, close fistulae and prevent relapse. Their mode of action likely depends on long-term cytostatic effects on immune effector cells. Concern for leukopenia and the development of late malignancy has limited their use to patients not responding to other therapies. Metronidazole, an antimicrobial agent that is effective against anaerobes, has recently been shown useful in Crohn's disease involving the colon and perianal area. Its mechanism of action is uncertain, but may be related to its antibacterial actions on anaerobes. Cholestyramine can be successfully used to control bile salt-induced diarrhea in Crohn's patients with terminal ileal resections. Effective drug therapy of inflammatory bowel disease is only part of a total program of management including reassurance, frequent explanation, well-timed use of surgery, and an understanding physician.