''The major finding was that all IBS symptoms improved," says Mark Pimentel, MD, director of the GI Motility Program at Cedars-Sinai Medical Center, Los Angeles, who led the clinical trial of the drug at Cedars.
IBS is considered a functional gastrointestinal disorder without a known physiologic cause, with the symptoms recurring and often worsened by stress. Existing treatment options -- diet and lifestyle modification, psychological therapy, and other drugs -- do not help all people with the condition.
With the new antibiotic treatment, Pimentel tells WebMD, many participants ''say they are 80% improved, 90% improved, that kind of results. The stool was more solid, the diarrhea goes away, and the bloating is much less."
That can translate to big changes in the lives of those with IBS, estimated to affect about 15% of adult Americans. With the drug treatment, Pimentel says, those with the IBS ''can enjoy social outings without the worry of having to run to the bathroom and having diarrhea."
Experts believe that those with IBS may have changes in their intestinal microorganisms, leading them to consider targeting these gut microorganisms to treat the condition.
They chose to study rifaximin because it is minimally absorbed and stays in the gut, so they thought it might perform better than the antibiotics widely absorbed by the body, which have produced mixed results for IBS patients.
Pimentel and colleagues conducted two parallel studies of the antibiotic. In both trials, known as TARGET 1 and TARGET 2, they assigned 600 IBS patients with mild to moderate diarrhea and bloating to take either a 550-milligram dose of rifaximin or a placebo three times a day for two weeks.