Medications

Pharmacologic, or drug, therapy is best used in irritable bowel syndrome (IBS) patients with moderate to severe symptoms which do not respond to physician counseling and dietary manipulations. First line treatment has traditionally been aimed at treating the most bothersome symptom because of the lack of effective treatment for the overall improvement of multiple symptoms in IBS patients. However, new therapies for IBS have been recently introduced and have been shown to effectively treat multiple symptoms of IBS.

Laxatives

A laxative is a medication that increases bowel function. There are four main classes of laxatives: fiber, osmotic laxatives, stimulant laxatives, and emollients. Because most current pharmacological treatments are aimed at improving only one IBS symptom, it is often necessary to use a combination of therapies for adequate treatment.

Dietary fiber is usually the first treatment method tried for constipation-predominant IBS. If fiber has been deemed ineffective by your doctor, osmotic or stimulant laxative therapy may be considered. Osmotic laxatives are poorly absorbed compounds that cause an influx of water into the small intestine and colon, thereby increasing stool bulk. Stimulant laxatives have a direct stimulating effect on the network of nerves in the large intestine and reduce absorption of water and electrolytes from gastrointestinal contents. Stimulant laxatives take effect within hours of ingestion. Emollients act as stool softeners.

Anticholinergic/Antispasmodic agents

After fiber preparations, antispasmodic agents are the next most commonly prescribed group of medications for the treatment of IBS. However, several studies do not provide firm evidence that these agents are efficacious in the IBS population as a whole. Only a few of these antispasmodics have been shown to be more effective than placebo in relieving abdominal pain in some persons (particularly if the symptoms occur soon after eating) in high quality clinical IBS trials but these are not currently available in the U.S.

Antidiarrheal agents

In IBS patients with diarrhea, antidiarrheal agents such as loperamide and diphenoxylate can be effective in decreasing bowel movement frequency, improving stool form by enhancing intestinal water and ion absorption, and increasing anal sphincter tone at rest. These physiologic actions seem to explain the improvement in diarrhea, urgency, and fecal soiling observed in patients with IBS. These medications do not typically relieve abdominal pain and may cause constipation.

Antidepressant medications

The rationale of using antidepressants in IBS may relate to several factors, such as the effects of these agents on gut motility and pain sensation as well as the prominent co-existance of IBS with psychologic distress symptoms. Low-dose tricyclic antidepressants (e.g., nortriptyline, amitriptyline, desipramine) have been shown to be efficacious in treating IBS, particularly in those with mainly diarrhea. They have multiple effects that can be beneficial in relieving abdominal pain and altering gut motility. Some of the newer serotonin-norepinephrine reuptake inhibitors (SNRI’s, e.g., duloxetine) have fewer side effects and may be helpful for IBS symptoms but are not as well studied. 

Novel serotonin agents

There are newer medications that have been shown to be efficacious in treating IBS in multi-center, high quality clinical trials. Two of these medications are peripheral serotonergic agents (i.e., they act on serotonin receptors in the body, which help transmit nerve messages within the gut). Serotonin (5-HT) is one of the substances that helps to regulate bowel function and there are a number of different types of 5-HT receptors. Alosetron (Lotronex) is a drug that works on one type of receptor in the gut and has been approved for the use in women with severe diarrhea-predominant IBS. It is only prescribed under restricted use due to rare but potentially serious side effects. The drug tegaserod (Zelnorm) works on a different type of receptor in the gut, which helps promote peristalsis, the coordinated muscle contractions that propel content through the gastrointestinal tract. Tegaserod has been shown to be effective for treating constipation symptoms. It was initially approved for use in women with IBS where constipation is the predominant bowel symptom, and subsequently in men and women with chronic constipation (without predominant abdominal pain) under the age of 65. Lotronex is a prescription medications intended for specific use under a doctor’s supervision; Lotronex is no longer available in the U.S.

Summary

Donate Now to IFFGD Go »

The effectiveness of various agents differs between individuals. A medication regimen must be carefully chosen by the patient and his or her physician.

Individuals who have not responded to lifestyle changes and careful use of medications should consider being evaluated by a physician who specializes in motility or stress-related gastrointestinal disorders. More complex medication regimens, and specialized motility and/or psychological screening can reveal specific conditions which may respond to treatment.