An antibiotic used for traveler’s diarrhea may be effective for treating irritable bowel syndrome, a study indicates. The syndrome is characterized by abdominal pain or discomfort associated with defecation and diarrhea or constipation.

Researchers at the University of Chicago and Cedars-Sinai Medical Center in Los Angeles recruited 87 volunteers aged 18-65 years who met the criteria for IBS. The patients, two thirds of whom were women, were randomly assigned to a 10-day course of either placebo or double-blind treatment with rifaximin (Xifaxan) 400 mg t.i.d. Ten weeks after completion of therapy, the patients who received rifaximin reported global improvements in overall symptoms and less bloating than those given placebo. Mean overall improvement for rifaximin patients was 36% vs. 21% for the placebo group. Side effects were minimal.

The cause of IBS remains elusive, but evidence suggests enteric bacteria are involved, which is why the researchers say they chose to try an antibiotic (Ann Intern Med. 2006;145:557-563).

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Rifaximin is a relatively new, nonabsorbable, broad-spectrum medication derived from the rifamycin family. Because the drug is gut-selective and <1% is absorbed, it has little or no therapeutic use beyond enteric infections.