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Study shows that targeted antibiotics lead to prolonged improvement in IBS symptoms

October 17, 2006

Researchers at Cedars-Sinai Medical Center have found that a nonabsorbable antibiotic - one that stays in the gut - can be an effective long-term treatment for irritable bowel syndrome (IBS), a disease affecting more than 20 percent of Americans.

The study, which appears in the October 17 issue of the Annals of Internal Medicine, is the first to demonstrate benefits from antibiotic use even after the course of treatment has ended, supporting previously published research that identified small intestine bacterial overgrowth as a cause of the disease.

The randomized, double-blind, placebo-controlled study involved 87 participants, all of whom met specific multinational guidelines for diagnosis of IBS. They received 400 mg of the antibiotic rifaximin three times a day for 10 days or a placebo. Participants completed an extensive symptom questionnaire at the start of the study and then weekly for 10 weeks following treatment. The questionnaire measured the severity of nine symptoms (abdominal pain, diarrhea, constipation, bloating, urgency, incomplete evacuation, mucus, sense of incomplete evacuation, and gas). Patients were also asked to provide a percent global improvement from 0 to 100 percent in their overall IBS symptoms.

Researchers found that the rifaximin not only led to significant improvement in global IBS symptoms during the 10 days it was administered, but also that the benefit continued for the 10 weeks of follow up when no antibiotic was given, showing sustained benefit.

"The fact that the benefit of the targeted antibiotic continued even after it was stopped provides evidence that the antibiotic was acting on a source of the problem: excess bacteria in the gut," said Mark Pimentel, M.D., director of the GI Motility Program at Cedars-Sinai and the study's principal investigator. "This finding offers a new treatment approach - and a new hope - for people with IBS."

Irritable Bowel Syndrome is one of the top 10 most frequently diagnosed conditions by U.S. physicians. It is an intestinal disorder that causes abdominal pain, cramping, bloating and diarrhea and/or constipation and is a long-term condition that usually begins in early adult life. Episodes may be mild or severe and may be exacerbated by stress. IBS is more common in women than in men.

"While this study being released today demonstrates that the non-absorbed antibiotic rifaximin has great promise in the clinical improvement of IBS, more research is needed," said Pimentel. "Next steps include multi-center studies to further assess short- and long-term benefits of this drug. Tests comparing rifaximin to other types of antibiotics that have been used to treat the disease should also be conducted."

Because the cause of IBS has been elusive, treatments for the disease have historically focused on reducing its symptoms - diarrhea and constipation - by giving medications that either slow or speed up the digestive process. In The American Journal of Gastroenterology (Dec. 2000), Pimentel linked bloating, the most common symptom of IBS, to bacterial fermentation by giving lactulose breath tests to participants. The test, which monitors the level of hydrogen and methane (the gases emitted by fermented bacteria) on the breath, showed evidence that small intestine bacteria overgrowth may be a causative factor in IBS.

Participants in the current Annals study also took the breath tests, which showed similarly increased levels of hydrogen and methane.

Cedars-Sinai Medical Center