TUESDAY, Oct. 17 (HealthDay News) -- Rifaximin, an antibiotic, appears to ease the discomfort of chronic irritable bowel syndrome (IBS), researchers report, and these healthy effects continue long after patients stop taking the drug.
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Rifaximin targets bacterial "overgrowth" in the small intestine. Some researchers believe this excess bacteria is the underlying cause of many, if not all, cases of IBS.
The antibiotic is already approved by the U.S. Food and Drug Administration (FDA) for the treatment of "traveler's diarrhea," a non-chronic condition that affects otherwise healthy men and women.
"The striking part is that IBS patients got better and stayed better over 10 weeks after taking rifaximin for only 10 days," said study author Dr. Mark Pimentel, director of the Gastrointestinal Motility Program at Cedars-Sinai Medical Center in Los Angeles. "This suggests that with the drug, we're actually doing something about what's causing IBS -- which we think is bacterial overgrowth in the bowels."
The study, conducted by Pimentel's team, was funded by Salix Pharmaceuticals, the North Carolina-based manufacturer of rifaximin, which markets the drug under the trade name Xifaxan.
However, the authors stated the drug company's sponsorship of the study "had no role in the collection, analysis, or interpretation of the data," which is published in the Oct. 17 issue of the Annals of Internal Medicine.
According to the U.S. National Institutes of Health, IBS affects the part of the digestive tract that is responsible for stool production. Impeded bowel functioning associated with the disorder can result in cramping, bloating, gas, diarrhea and constipation.
There's no cure for IBS at present. However, the disorder is typically treated with a combination of dietary alterations (eliminating foods such as caffeine, alcohol, sodas, dairy and high-fat foods), medicines (laxatives, antispasmodics and antidepressants) and stress counseling.
Some success has also recently been reported with the use of a newer class of biologic therapies, including lubiprostone (Amitiza), that target IBS-linked inflammation.
Unlike other antibiotics, rifaximin has minimal side effects because it is not absorbed into the blood stream. Instead, it stays in the gut, where it does its job killing bacteria before passing through the digestive tract.
None of the patients had conditions other than IBS associated with bacterial overgrowth, and none had been taking any antibiotics in the prior three months leading up to the study.
Half of the group was prescribed a 400-miligram dose of rifaximin three times daily for 10 days, while the other half received a placebo.
Prior to the onset of the drug regimen, weeklong stool "diaries" were maintained and symptom questionnaires were completed by all patients regarding any incidences of diarrhea, constipation, abdominal pain and bloating.
After the 10-day period elapsed, no more medication was offered. Another weeklong diary was then completed for the initial post-drug week, followed by completion of a once-weekly symptom questionnaire for the ensuing nine weeks. All patients visited a clinic for an exam at the end of the full 10-week post-medication period.
Pimentel and his associates observed that, at the time of the 10-week evaluation, roughly 37 percent of the rifaximin-taking patients had experienced a greater than 50 percent improvement in their IBS symptoms overall.
In contrast, just 15 percent of patients on placebo demonstrated a similar diminishment in symptoms.
Viewed from a different perspective, the antibiotic group self-reported an average improvement in their IBS condition of about 36 percent, while the non-antibiotic group showed an average improvement of just 21 percent, the researchers said.
Side effects were rare and included abdominal pain, diarrhea and a bad taste in the mouth, the researchers reported.
The antibiotic appeared to work primarily by easing bloating. According to the researchers, bloating was the only symptom to significantly diminish in severity for patients taking rifaximin vs. those taking placebo.
Pimentel's team called for larger, longer-term studies to better explore rifaximin's potential side effects, as well as its benefits for IBS sufferers, and to stack the drug's effectiveness up against other IBS treatments.
"Patients need to start to gain hope, because with this work, we are approaching the true causes for IBS," Pimentel said. "And if we can deal with more causative factors, we'll have more permanent approaches to treating IBS down the road. And I think that's what we're really shooting for over the next five to 10 years."
However, in an accompanying editorial in the journal, Dr. Douglas A. Drossman, of the Center for Functional GI and Motility Disorders at the University of North Carolina in Chapel Hill, was somewhat less optimistic.
He noted that rifaximin did not help reduce pain, diarrhea or constipation, and he questioned the researchers' assumption that about three-quarters of IBS patients have a bacterial overgrowth problem. According to Drossman, other studies have suggested that that figure may be as low as one in 10.
Another expert was more supportive, however.
"Yes, there has been enormous resistance to the idea that a fairly large percentage of IBS patients have an overgrowth of intestinal bacteria," agreed Dr. Maria Abreu, director of the Inflammatory Bowel Disease Center and an associate professor of medicine at Mount Sinai Medical Center in New York City. "And I do think it'll be important to define which subgroups of patients really respond particularly well to this antibiotic and perhaps, in the future, to other antibiotics."
"But," she added, "I also think that this is an important proof of principal that if you have an antibiotic that is broad enough and potent enough so it stays in the GI tract to lower the bacterial concentration sufficiently, you can certainly make some headway against IBS."
SOURCES: Mark Pimentel, M.D., director, Gastrointestinal Motility Program, Cedars-Sinai Medical Center, Los Angeles, Calif; Douglas A. Drossman, M.D., Center for Functional GI and Motility Disorders, University of North Carolina, Chapel Hill; Maria Abreu, M.D., director, Inflammatory Bowel Disease Center, and associate professor, medicine, Mount Sinai Medical Center, New York City; Oct. 17, 2006, Annals of Internal Medicine
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