Rifaximin considered as possible treatment for IBS

Rifaximin has demonstrated global improvement of the symptoms of irritable bowel syndrome (IBS) in patients for ≤ 10 weeks after the discontinuation of therapy. Rifaximin is a nonabsorbed (≤ 0.4%), broad-spectrum antibiotic that was approved by FDA in 2004 for travelers' diarrhea.

In this small, double-blind, randomized study published in the Annals of Internal Medicine, 87 patients (29 men, 58 women) with IBS received either rifaximin 400 mg 3 times/d (n=43; mean age, 39.1 years) or placebo (n=44; mean age, 38.2 years) for 10 days. The primary end point was global improvement in IBS symptoms during follow-up.

Initial assessment included 7-day stool diaries and symptom questionnaires that asked patients to indicate the severity of abdominal pain, diarrhea, constipation, bloating, urgency, incomplete evacuation, mucus, sense of incomplete evacuation, and gas using a visual analogue scale (VAS) ranging from 0 mm to 100 mm (extreme). Although breath testing and breath methane level determinations were also performed, the authors did not include this information in their report. In the follow-up phase of the trial, patients were asked to provide a weekly estimated percentage of global improvement in their overall IBS symptoms. During follow-up, patients also completed 9 weekly self-administered symptom questionnaires.

Secondary analysis evaluating individual bowel symptoms demonstrated significantly better scores for bloating among rifaximin recipients during follow-up compared with bloating VAS scores among placebo recipients (P=.010), but scores for abdominal pain (P=.32), diarrhea (P=.67), and constipation (P=.069) did not differ significantly.

In an accompanying editorial, Douglas A. Drossman, MD, was critical of the study's findings. Dr Drossman stated, "While one could conclude from the study that rifaximin could be beneficial for treating bloating and global symptoms in IBS, the limitations of the study make the findings inconclusive and raise questions about the clinical significance of the results." The limitations identified by Dr Drossman included the exclusion of breath test results, vast differences in sample sizes at the 2 study sites (83 vs 3 participants), a nontraditional primary outcome measure and method of analysis, imbalance in baseline pain scores, and lack of improvement in secondary end points other than bloating.

The authors addressed some of these limitations in their paper, noting that a larger, longer study would be beneficial. However, they said the demonstrated benefits of rifaximin on IBS are significant and worthy of further studies comparing antibiotics with other IBS treatment strategies.

SOURCES Pimentel M, Park S, Mirocha J, Kane SV, Kong Y. The effect of a nonabsorbed oral antibiotic (rifaximin) on the symptoms of the irritable bowel syndrome. Ann Intern Med. 2006;145:557–563.

Drossman DA. Treatment for bacterial overgrowth in the irritable bowel syndrome[editorial]. Ann Intern Med. 2006;145:626–628.