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Another Small Step Forward in Treating Patients with IBS

Rifaximin helps control bloating symptoms in some IBS patients.

The etiologies of irritable bowel syndrome (IBS) and the mechanisms by which symptoms are produced vary but include disorders of gut motility, secretion, and sensation. In addition, small-intestinal motility disorders can result in small-intestinal bacterial overgrowth (SIBO), which can lead to abdominal pain, distension, and diarrhea — all cardinal symptoms of IBS. IBS patients have a high prevalence of SIBO, and a few studies have indicated that some IBS symptoms improve with antibiotic therapy, albeit with side effects. In this study, investigators sought to determine whether treatment with a new nonabsorbable and well-tolerated antibiotic, rifaximin (Xifaxan), would improve symptoms in patients with IBS.

Researchers enrolled 87 patients with IBS (Rome I criteria) in this placebo-controlled, randomized, double-blind, industry-sponsored U.S. study. Patients received either thrice-daily rifaximin (400 mg/dose) or placebo for 10 days. Overall, treatment was well tolerated, and side effects were mild. Global symptom outcomes were assessed for 10 weeks. Specific symptoms also were evaluated.

At 10 weeks, global symptoms improved by 36% in the rifaximin group and by 21% in the placebo group. The authors did not provide information on rates of complete, or even partial, relief or on whether a finding of SIBO (based on breath tests prior to therapy) correlated with symptom improvement. In the secondary analysis, evaluation of specific symptoms indicated that improvement was isolated to bloating; abdominal pain and diarrhea did not improve.

Comment: What do these findings mean to the clinician? First, we have few robust therapies for IBS — in general, response to other approved (or likely to be approved) agents for this disorder, such as tegaserod (Zelnorm), lubiprostone (Amitiza), or alosetron (Lotronex), is modest at best. Thus, some patients likely would benefit from new therapies such as rifaximin. Treatment effects with this agent are limited to improving symptoms of bloating, and no information was provided to allow us to quantify the therapeutic response or the number of patients with marked or complete improvement.

Second, these findings suggest that SIBO can play a role in IBS symptoms and that development of effective therapies for SIBO would be beneficial for some patients. However, SIBO is not a disease; rather, it is a consequence of ineffective small-intestinal motility, and the underlying dysmotility will still exist after SIBO is eliminated. One would hypothesize that SIBO and IBS symptoms will reoccur in most patients who initially respond and that retreatment or chronic therapy for SIBO will be required.

Third, the safety and cost of long-term or repeated therapy for SIBO is unknown, and we must be cautious about embracing emerging therapies before we understand the long-term outcomes. An intriguing possibility is to use antibiotics and prokinetic therapies in combination, but this approach has not been investigated. Despite all these caveats, these findings present a glimmer of hope that effective therapies for IBS exist, even though the disorder has frustrated patients and physicians because of limited ability to achieve symptom responses with current therapies.

— M. Brian Fennerty, MD

Published in Journal Watch Gastroenterology October 16, 2006

Citation(s):

Pimentel M et al. The effect of a nonabsorbed oral antibiotic (Rifaximin) on the symptoms of the irritable bowel syndrome: A randomized trial. Ann Intern Med 2006 Oct 17; 145:557-64.

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