Irritable bowel syndrome (IBS) is characterized by recurrent abdominal discomfort or pain that is accompanied by at least two of the following: relief by defecation, change in frequency of stool, or change in consistency of stool.
IBS can be classified as either diarrhea-predominant (IBS-D), constipation-predominant (IBS-C), or with alternating stool pattern (IBS-A) or pain-predominant). In some individuals, IBS may have an acute onset and develop after an infectious illness characterized by two or more of the following: fever, vomiting, diarrhea, or positive stool culture. This post-infective syndrome has consequently been termed “post-infectious IBS” (IBS-PI).
The primary symptoms of IBS are abdominal pain or discomfort in association with frequent diarrhea or constipation and a change in bowel habits. There may also be urgency for bowel movements, a feeling of incomplete evacuation , bloating, or abdominal distension.
People with IBS, more commonly than others, have gastroesophageal reflux, symptoms relating to the genitourinary system, chronic fatigue syndrome, fibromyalgia, headache, backache and psychiatric symptoms such as depression and anxiety.
Cognitive-behavioral therapy, standard psychotherapy, and hypnotherapy may help some IBS patients.
- Drug therapy is directed toward the dominant symptoms.
- Anticholinergic drugs (eg,hyoscyamine 0.125 mg po 30 to 60 min before meals) may be used for their antispasmodic effects.
- Tegaserod, a 5HT4 agonist, stimulates motility and alleviates constipation, it slightly increased the incidence of cardiovascular ischemic events (ie, MI, unstable angina pectoris, stroke) compared with placebo.Tegaserod has since been used under a restricted program.
- The chloride channel activator lubiprostone and the guanylate cyclase C agonist linaclotide may help patients with constipation.
- In patients with diarrhea, oral diphenoxylate 2.5 to 5 mg or loperamide 2 to 4 mg may be given before meals. The dose of loperamide should be titrated upward to reduce diarrhea while avoiding constipation.
- For many patients, tricyclic antidepressants (TCAs) help relieve symptoms of diarrhea, abdominal pain, and bloating. These drugs are thought to reduce pain by down-regulating the activity of spinal cord and cortical afferent pathways arriving from the intestine.
- Treatment should begin with a very low dose of a TCA (eg,desipramine 10 to 25 mg once/day at bedtime), increasing as necessary and tolerated up to about 100 to 150 mg once/day. SSRIs are also useful, particularly for patients with anxiety or an affective disorder, but may exacerbate diarrhea.
- 5HT3 antagonists (eg, alosetron) may benefit female patients with severe diarrhea refractory to other drugs. Because alosetron is associated with ischemic colitis, its use is restricted.
- Preliminary data suggest that certain probiotics (eg, Bifidobacterium infantis) alleviate IBS symptoms, particularly bloating.
- Certain aromatic oils (carminatives) can relax smooth muscle and relieve pain caused by cramps in some patients. Peppermint oil is the most commonly used agent in this class.
- Meals should not be overly large, and eating should be slow and paced.
- Patients with abdominal distention and increased flatulence may benefit from reducing or eliminating beans, cabbage, and other foods containing fermentable carbohydrates.
- Reduced intake of sweeteners (eg, sorbitol, mannitol, fructose), which are constituents of natural and processed foods (eg, apple and grape juice, bananas, nuts, and raisins), may alleviate flatulence, bloating, and diarrhea.
- Patients with evidence of lactose intolerance should reduce their intake of milk and dairy products.
- A low-fat diet may reduce postprandial abdominal symptoms.
- Dietary fiber supplements may soften stool and improve the ease of evacuation.
- A bland bulk-producing agent may be used (eg, raw bran, starting with 15 mL [1 tbsp] with each meal, supplemented with increased fluid intake). Alternatively, psyllium hydrophilic mucilloid with two glasses of water may be used. However, excessive use of fiber can lead to bloating and diarrhea, so fiber doses must be individualized. Occasionally, flatulence may be reduced by switching to a synthetic fiber preparation (eg, methylcellulose).