Antibiotic May Aid Irritable Bowel

Ten days' treatment with the antibiotic Xifaxan reduces symptoms of irritable bowel syndrome (IBS), a small clinical trial suggests.

IBS is a condition of the intestinal tract that causes symptoms of bloating, gas, abdominal cramping, diarrhea, and constipation.

Xifaxan, now approved for the treatment of travelers' diarrhea, kills bacteria living in the gut. Experts disagree over the cause of IBS. Some suspect the root cause to be overgrowth of gut bacteria.

One of these experts is Mark Pimentel, MD, director of the gastrointestinal motility program at Cedars-Sinai Medical Center in Los Angeles. In prior studies, Pimentel used breath tests to show that about 80% of IBS patients may have serious bacterial fermentation going on in their gut.

This led him to wonder what would happen if he used a powerful antibiotic to shift the balance between overgrowth of these theoretically harmful bacteria and normal bacteria living in the gut.

So Pimentel and colleagues gave a 10-day course of Xifaxan or inactive placebo to 87 IBS patients. Seventy-two patients finished the study. As is common in IBS studies, those who got placebo felt a bit better. Those who got Xifaxan reported even more improvement -- especially less bloating.

"Xifaxan was superior to placebo for control of IBS," Pimentel tells WebMD. "It suggests we are finally tackling a sustainable cause of IBS. If it is bacteria, we have changed the environment so that IBS is better on a semipermanent basis."

The study, funded by Xifaxan maker Salix Pharmaceuticals, appears in the Oct. 17 issue of Annals of Internal Medicine. Pimentel is a consultant to Salix and has received speaking fees from the company. Cedars-Sinai Medical Center has a licensing agreement with Salix.

Change of IBS Treatment?

Is Xifaxan a new treatment for IBS? Not yet. A larger study, looking at IBS patients treated by their own doctors with Xifaxan, is already underway. Until those results are known, Xifaxan is not an officially approved treatment for IBS.

But Pimentel says he's treated "thousands" of IBS patients with Xifaxan -- and he says now the word is getting out.

"The gem here is you have a sustained effect in IBS. The larger, longer studies will show how well this works," he says. "We've reported these results at professional meetings, and it has changed the way IBS is treated. Sixty percent of gastroenterologists in the country are starting to do it this way."

Pimentel says the average patient needs re-treatment every two or three months, but that response varies greatly from patient to patient.

Controversy Over IBS Treatment

Not all experts are convinced that bacterial overgrowth is a root cause of IBS, or that antibiotics are the best treatment. One of these experts is Douglas A. Drossman, MD, co-director of the University of North Carolina Center for Functional GI and Motility Disorders, Chapel Hill.

In an editorial accompanying the Pimentel study, Drossman notes that IBS is a complex disorder that springs from the complex interplay of an oversensitive gut and the brain.

Breath tests, he says, aren't reliable for diagnosing bacterial overgrowth. And Pimentel's study, he says, does not prove that treating bacterial overgrowth helps.

Drossman is not impressed by Pimentel's finding that IBS patients reported an average 36.4% improvement in the 10 weeks after treatment with Xifaxan, while those given placebo treatment reported an average 21% improvement.

"Only bloating improved, and abdominal pain, diarrhea, and constipation did not improve," Drossman notes. "The benefit of using antibiotics is not fully proven and must be balanced with potential risks in terms of side effects, high costs -- a 10-day course of Xifaxan is $250 -- and a breath test, if ordered, costs an additional $304, and the need for recurrent treatment."

Pimentel says new studies now coming out will support the bacterial-overgrwth theory of IBS. He does, however, say people with IBS have "movement disorders of the small bowel." He is hoping that a drug to promote movement in the small bowel will improve outcomes for IBS patients treated with antibiotics.

SOURCES: Pimentel, M. Annals of Internal Medicine, Oct. 17, 2006; vol 145: pp 557-563. Drossman, D.A. Annals of Internal Medicine, Oct. 17, 2006; vol 145: pp 626-628. Mark Pimentel, MD, director, gastrointestinal motility program, Cedars-Sinai Medical Center, Los Angeles.