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Because patients with irritable bowel syndrome (IBS) can have alterations in bacterial bowel flora, antibiotic therapies have been proposed. To investigate whether antibiotic therapy is effective, industry-supported researchers randomized 1260 IBS patients with abdominal pain and bloating (but without constipation) to receive 2-week courses of either rifaximin (Xifaxan) or placebo. Rifaximin is a minimally absorbed antibiotic that is FDA-approved for treatment of travelers' diarrhea and prevention of hepatic encephalopathy.
The primary endpoint (patient-reported “adequate relief” of IBS symptoms during at least 2 of the 4 weeks following treatment) was noted by 41% of rifaximin recipients and by 32% of placebo recipients — a significant difference. Outcomes were similar for relief of bloating specifically. During 6 additional weeks of observation, the proportion of responders declined in both groups but remained higher in the rifaximin group than in the placebo group. No serious adverse effects occurred.
Pimentel M et al. Rifaximin therapy for patients with irritable bowel syndrome without constipation. N Engl J Med 2011 Jan 6; 364:22. (http://dx.doi.org/10.1056/NEJMoa1004409)
Comment
A 2-week course of rifaximin relieved IBS symptoms in some patients during the month after treatment. The 9-percentage-point difference in response between rifaximin and placebo means that 11 patients must be treated to benefit 1 patient. Because benefit was modest, follow-up was brief in this chronic condition, and concern exists that widespread use of rifaximin could promote bacterial resistance, longer-term efficacy and safety data are necessary before rifaximin can be added to the list of IBS treatments.