Salix Pharmaceuticals funded the research, a phase 3 clinical trial. The company has applied for U.S. Food and Drug Administration approval for the medication, which is currently approved for treating traveler's diarrhea and hepatic encephalopathy, a brain disorder caused by liver disease.
Another benefit of rifaximin, Ringel said, is that it's poorly absorbed by the body, meaning that it passes through the stomach into the intestines and is excreted in the stool instead of being absorbed into the bloodstream.
That means there's less risk for side effects than there is with antibiotics that are absorbed systemically, said Dr. Jan Tack, a professor of medicine and head of the Translational Research Center for Gastrointestinal Disorders at the University of Leuven in Belgium, who wrote an accompanying editorial.
"Rifaximin looks promising and has a number of attractive features," Tack said. "IBS is a very prevalent condition, and the number of therapies of proven efficacy is very very limited. There is clearly a need for new therapies."
As many as 20 percent of Americans have symptoms of IBS, a recurring condition that can include cramping, abdominal pain, bloating and a change in stool consistency and frequency, such as constipation and diarrhea, according to the U.S. National Digestive Diseases Information Clearinghouse.
Though uncomfortable and distressing, IBS does not harm the intestines and does not raise the risk for other diseases, such as cancer, Ringel said.
The cause of IBS is unknown. Researchers have not been able to determine a specific abnormality, such as an infection or inflammation, that explains it.
Dietary changes and stress reduction help many people. Doctors also sometimes suggest anti-diarrheal medications, medications to relieve bloating and constipation
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