A targeted antibiotic provides effective and long-lasting relief of Irritable Bowel Syndrome symptoms, according to the results of two multisite Phase III clinical trials designed by Cedars-Sinai researchers. Rifaximin is the first drug treatment for IBS that relieves symptoms while it's being administered and continues to benefit patients after they stop taking the drug.

Researchers found that patients who took rifaximin not only experienced relief of their IBS symptoms, including specific symptoms of bloating, abdominal pain and stool consistency, while they were taking the antibiotic, but also that their relief was sustained over the 10 week follow-up period when no antibiotic was administered.

The results of the studies were presented at the Digestive Disease Week conference in New Orleans on May 3.

"These studies validate the role of altered gut bacteria in IBS," said Mark Pimentel, M.D., GI Motility Program director at Cedars-Sinai and the principal investigator of the clinical trail at Cedars. "These findings show that targeted antibiotics provide safe and long-lasting improvement for IBS patients."

IBS is the most common gastrointestinal disorder in the United States, affecting more than 20 percent of the population. Traditionally, patients with IBS have been described as having "constipation predominant," "diarrhea-predominant" or an alternating pattern of diarrhea and constipation. In addition to these symptoms, IBS patients often experience abdominal pain or cramps, excess gas or bloating, harder or looser stools than normal and visible abdominal distension.

Because the cause of IBS has been elusive, treatments for the disease have historically focused on relieving its symptoms through medications that either slow or speed up the digestive process. Earlier research conducted by Pimentel and colleagues documents a possible link between bloating, the most common IBS symptom, and bacterial fermentation by giving participants lactulose breath tests. The test monitors the level of hydrogen and methane -- the gases emitted by fermented bacteria -- on the breath. Those tests show elevated levels of those gases, indicating that small intestine bacterial overgrowth, or SIBO, may be a cause of IBS.

More than 1,200 patients participated in the Phase III, double-blind, multi-center studies of rifaximin, a nonabsorbable antibiotic that stays in the gut and is currently FDA-approved to treat traveler's diarrhea and hepatic encephalopathy. IBS patients with mild to moderate diarrhea and bloating were randomized to receive 550 milligrams of rifaximin or placebo for two weeks. Patients were then followed for an additional 10 weeks. Phase III trials are randomized studies on large patient groups to definitively demonstrate the safety and effectiveness of a new drug.

The findings support previous research by Pimentel indicating that IBS is caused by an overgrowth of bacteria in the gut.

"Even after you stop the antibiotic, the patients continue to feel better, which indicates that we did something to strike at what causes the condition," Pimentel said.

In addition to Cedars-Sinai, other centers participating in the clinical trials included Beth Israel Deaconess Medical Center in Boston, University of Michigan Medical Center in Ann Arbor, University of North Carolina at Chapel Hill, Connecticut Gastroenterology Institute in Bristol, Conn.

Rifaximin is marketed by Salix Pharmaceuticals, Inc. Salix also provided funding for the studies. Pimentel discovered the use of rifaximin for IBS, and Cedars-Sinai holds patent rights to this discovery and has licensed rights to the invention to Salix. Dr. Pimentel is a consultant to Salix, Inc, and serves on its scientific advisory board.