Antibiotic May Ease Irritable Bowel Syndrome

January 5, 2011


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By Amanda Gardner

WEDNESDAY, January 5 ( — An antibiotic widely used to treat diarrhea in travelers may also provide some relief to people with the common and difficult-to-treat condition known as irritable bowel syndrome (IBS), according to a pair of new studies in the New England Journal of Medicine.

The Food and Drug Administration (FDA) has not yet approved the antibiotic, rifaximin, for use in IBS, which affects as many as 1 in 5 U.S. adults. The agency is currently reviewing the drug for that purpose and is expected to make a decision in March.

In the studies, 1,200 IBS patients took rifaximin or a placebo pill three times a day for two weeks. Roughly 40% of the patients who took the antibiotic reported substantial relief from symptoms such as bloating, abdominal pain, and loose stools for at least two weeks during the subsequent month, compared to a little under one-third of the patients taking placebo. All of the patients in the studies had a form of IBS that does not involve constipation.

“It made all the symptoms of irritable bowel syndrome better, which we don’t see too often in studies,” says the lead researcher, Mark Pimentel, MD, a gastroenterologist at Cedars-Sinai Medical Center, in Los Angeles.

The studies were funded by the maker of rifaximin, Salix Pharmaceuticals, which was also involved in collecting and analyzing the data. (This arrangement isn’t unusual in these types of studies, which are known as phase 3 trials and are generally the last research step in the FDA approval process.) In addition, Dr. Pimentel and several of his co-authors report financial relationships with Salix, including receiving consulting fees from the company.

Rifaximin, sold under the brand name Xifaxan for travelers’ diarrhea, appears to be safe and doesn’t seem to foster resistance among gut bacteria, meaning it can be used over and over, Dr. Pimentel says. That could be important, because the number of study participants who reported lasting relief from their two-week rifaximin regimen gradually declined in the 10 weeks following treatment.

Next page: “No good options” for treating IBS

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