Click here to view next page of this article

IRRITABLE BOWEL SYNDROME

Irritable bowel syndrome (IBS) is the most common functional disorder of the gastrointestinal tract. As a result of the lack of specific diagnostic testing and absence of circumscribed biologic markers of disease, the diagnosis is based on a constellation of symptoms irritable bowel syndrome. In an attempt to standardize the definition of disease, an international consensus group formalized clinical parameters based on data from Manning et al.

Symptoms of IBS have afflicted humans since antiquity. Maimonides advised that humans should strive to have their intestines relaxed all the days of their lives. IBS is a common disorder.

Based on the large portion of the population affected, the societal costs of the disease are immense. Physician visits total approximately 3.5 million a year, and medications are prescribed for most patients, averaging 2.2 million prescriptions a year.

TREATMENT

Successful treatment of the patient with IBS depends on attention to many essential factors. Dietary understanding and manipulation may be helpful. Patients with suspected lactase deficiency should exclude lactose-containing items from their diet to assess if there is a clinical response. Some patients note improvement with avoidance of other forms of sugar, including sorbitol and fructose. Restriction of gas-producing foods may be beneficial in reducing.

A high-fiber diet or fiber supplementation may ease symptoms in patients with disease associated predominantly with constipation. Constipation may improve by the effect of fiber on colonic transit. Gradual introduction of fiber may diminish the common complaint of gas and bloating from these agents. Despite the nearly universal recommendation of adding fiber to the diet, however, its role in symptom control is unproven.

Stimulant laxatives should be avoided, in part, because they cause diarrhea or irregular bowel movements and to reduce the potential for short-term and long-term adverse effects. For patients with medically defined diarrhea, antidiarrheal agents are useful. The patient's account of bowel movements should be reviewed, however, because many individuals misinterpret the occurrence of frequent stools.

Loperamide may be helpful in selected patients and contribute to improvement in stool consistency, reduction in frequency of defecation, and amelioration of daytime abdominal pain. An increase in resting tone of the anal canal may explain partially these results. Prophylactic administration of loperamide before anticipated circumstances of symptoms.

Anticholinergics, including dicyclomine and hyoscine, have been the cornerstone of therapy for many patients. Data from clinical trials evaluating these therapeutic agents are difficult to assess and compare because of research design, significant dropout rates, high placebo response rates, subjectivity of responses.

Newer agents, including zamifenacin and darifenacin, are undergoing study for efficacy and safety. In animals, zamifenacin, a M3 receptor antagonist, decreases small and large bowel motility but accelerates gastric emptying. In a multicenter, double-blind, parallel group, placebo-controlled study, zamifenacin attenuated the postprandial colonic reflex in patients with IBS. Darifenacin has enhanced M3 selectivity with reduced affinity for M1 (gastric acid) and M2 (heart rate) receptors, possibly improving its side-effect profile. Further studies are under way. In general, although anticholinergic agents are frequently used as antispasmodics, scientific evaluation has been limited in evaluating their efficacy, and their use may be limited.

Low doses of antidepressants, especially tricyclic antidepressants, are advantageous in some patients. Psychotropic drugs are most useful in disease associated predominantly with diarrhea and for those with clinically significant psychologic features. Although these agents were initially thought to be beneficial because of their anticholinergic effects, the current hypothesis implicates an impact on afferent nerves.

Psychotherapy and related psychologic therapies are helpful in some patients, especially those with a psychiatric diagnosis. Anxiety and depression may improve, in addition to a reduction of abdominal symptoms, with psychotherapy.

Ongoing research studies using a novel group of pharmacologic agents that bind to serotonin receptors are proving promising in the treatment of IBS, particularly those that bind to 5-hydroxytryptamine (5-HT)₃ and 5-HT₄ receptor sites. Prucolopride and tegaserod are primarily 5-HT₄ agonists that effect midgut and distal gut activity. In contrast, 5-HT₃ antagonists accelerate intestinal transit and attenuate visceral sensitivity. In double-blind, placebo-controlled studies of ondansetron, subjective and objective symptoms improved. These agents may benefit particularly the subset of patients.