Irritable bowel syndrome (IBS) can be a frustrating condition for many patients due to its chronic nature and the lack of definitive therapies. Previous small trials have suggested that rifaximin (Xifaxan) may provide some relief of IBS symptoms. Two large, identically-designed randomized trials provide further evidence for the efficacy of rifaximin in patients without constipation. A total of 1,260 adults (mean age 46 years) who had IBS (by Rome II criteria) without constipation were randomized to rifaximin 500 mg orally 3 times daily vs. placebo for 2 weeks and were then followed for an additional 10 weeks. The primary outcome was adequate relief of IBS symptoms for at least 2 weeks during the 4-week period immediately following treatment. Relief was assessed by response to weekly yes/no questions regarding symptom improvement. In an analysis pooled across the 2 trials, global IBS symptoms were adequately relieved in 40.7% of the rifaximin group vs. 31.7% of controls (p < 0.001, NNT 12) (level 1 [likely reliable] evidence). The rifaximin group also had greater relief of IBS-related bloating (40% vs. 30.3%, p < 0.001, NNT 11). Additionally, rifaximin was associated with significantly increased relief of global symptoms, bloating, and abdominal pain over the whole 12-week study period. There were no significant differences in adverse events (N Engl J Med 2011 Jan 6;364(1):22). The medication is expensive, so its role in treating IBS may depend on whether the improvement in symptoms is maintained significantly beyond 12 weeks.
For more information, see the Irritable bowel syndrome (IBS) topic in DynaMed.