Antibiotic effective in treating irritable bowel syndrome, study finds

A two-week treatment with an antibiotic can ease overall symptoms in many patients with irritable bowel syndrome for at least 10 weeks and perhaps for much longer, according to a pair of clinical trials of more than 1,200 patients reported Wednesday.

The proportion of patients who benefited — about 11% — was modest, but the fact that any at all were helped validated the idea that intestinal bacteria play a role in the onset of irritable bowel syndrome, commonly known as IBS, said Dr. Mark Pimentel of Cedars-Sinai Medical Center in Los Angeles, who led the study published in the New England Journal of Medicine.

“This is the culmination of a 10-year journey in proving that gut bacteria are a cause of IBS,” he said. “There has been a lot of skepticism, a lot of criticism.”


The drug used in the trials, rifaximin, “has the potential to provide a welcome addition to the limited armamentarium of agents that are available to treat IBS,” Dr. Jan Tack of the University of Leuven in Belgium wrote in an editorial accompanying the report.

Rifaximin, which is already approved to treat travelers’ diarrhea and a liver condition called hepatic encephalopathy, is an appealing antibiotic for the purpose, Tack said, because it does not leave the gut and get into the general circulation, does not appear to promote resistance and has few, if any, side effects.

Irritable bowel syndrome, which affects 10% to 20% of the population, is characterized by abdominal discomfort, bloating and abnormal bowel movements. Some patients suffer constipation, others suffer diarrhea and still others alternate between the two. The pain can be severe, even disabling, but is usually relieved temporarily by passing gas or a bowel movement.

Pimentel’s previous studies have suggested that at least some forms of the disorder are caused when the small intestine is overgrown by bacteria that ferment sugars to produce excessive amounts of gas, which can cause pain. Preliminary studies suggested that rifaximin, which is sold by Salix Pharmaceuticals Inc. under the brand name Xifaxin, could kill off the bacteria, easing symptoms.

In the two identically designed trials, a total of 1,260 patients with IBS without constipation were randomly assigned to receive either rifaximin or a placebo for two weeks and then monitored for an additional 10 weeks.

About 41% of the patients receiving rifaximin reported relief from bloating, abdominal pain and loose or watery stools, compared with 30% of those receiving the placebo. That relief lasted for the entire 10 weeks of follow-up.

“Every other drug that has been used for IBS, once you stop, the symptoms start right back up,” Pimentel said. “With this one, the patient has lasting benefits.”

Cedars-Sinai holds a patent on the use of rifaximin for treating IBS and has licensed the rights to Salix, which funded the trial. Pimentel consults for Salix and sits on the company’s scientific advisory board.

Dr. Edward J. Share, a gastroenterologist at Cedars-Sinai who was not involved in the trial, said he had already been using the drug for his patients “and a lot of patients’ lives are turned around.”

Pimentel is now conducting a trial of the drug on IBS patients with constipation. Results are expected in about a year.