Pharmacologic treatment

On the whole, treatment is more efficacious for individual symptoms of IBS than for global symptoms. There are no randomized controlled trial (RCT) data on laxatives in IBS, but a single small study suggests improvement in constipation with polyethylene glycol. Two RCTs of loperamide for IBS-D found it to be effective for diarrhea but not bloating, pain, or other symptoms.

For overall symptoms, there is evidence of a beneficial effect of antispasmodic medications and peppermint oil (which appears to relax smooth muscle). The studies, however, are generally older and short-term.

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There is now a fairly substantial body of data showing antidepressants to be superior to placebo for IBS symptoms including abdominal pain. The anticholinergic effects of tricyclics may give them particular value in IBS-D, while selective serotonin reuptake inhibitors appear to be a better choice when constipation predominates.

The 2009 review includes two important additions to the clinician’s armamentarium. Lubiprostone, the most recently approved IBS drug, is effective for global symptoms in women with IBS-C as well as for constipation itself. No alarming adverse effects have emerged with lubiprostone, but the guidelines caution against prescribing the drug to patients with mechanical bowel obstruction or preexisting diarrhea. Lubiprostone is not recommended in men, pending further research.  

The review also reports that the nonabsorbable antibiotic rifaximin was shown effective for global IBS symptoms in three RCTs. “Based on these results, rifaximin is most likely to be efficacious in IBS-D patients or IBS patients with a predominant symptom of bloating,” the authors say. Since bloating is common and difficult to treat, “this is a real advance,” according to Dr. Brandt. There are, however, no data to support long-term safety and effectiveness.

Two drugs included in the 2002 review became less available after the emergence of severe adverse effects. Alosetron has been shown to relieve abdominal pain and urgency in IBS-D in women and subsequently in men. Concerns about severe complicated constipation and ischemic colitis led to its temporary removal from the market. It is once again available through an FDA-administered prescribing program.

“Alosetron is a very effective drug for patients with diarrhea; it works when they can’t get relief from anything else, and also relieves global symptoms,” says Dr. Brandt. The drug is underused, and “nothing to be frightened about,” he continues. “If you don’t give it to patients with a history of ischemic colitis and follow the guidelines for the monitored program, patients do well.”

Shortly before the 2002 guidelines were written, tegaserod was approved on the basis of RCTs that found it effective for global symptoms in women with IBS-C. The drug was withdrawn following reports of heightened cardiovascular risk and is now available only by application to the FDA under an emergency investigational new drug protocol.

Nonpharmacologic treatments

A number of psychological therapies have been used to treat IBS. RCT data indicate that cognitive behavioral therapy (CBT), dynamic psychotherapy, and hypnotherapy are more effective than usual care for global symptoms of the condition but that relaxation therapy is not. CBT has been most thoroughly studied and showed clear benefits in a large 12-week trial.

There is some RCT evidence of the benefits of Chinese herbal therapy, but the authors point out that heterogeneity of components among various products makes a meaningful meta-analysis impossible, and significant concerns about toxicity remain. Trials of acupuncture have been inconclusive.

The American College of Gastroenterology’s Evidence-Based Systematic Review on the Management of Irritable Bowel Syndrome was published in The American Journal of Gastroenterology (2009; 104:S1-S35). It is available online (accessed January 5, 2010).

Mr. Sherman is a freelance medical writer in New York City.