Background: Irritable bowel syndrome (IBS) is a gastrointestinal disorder that is characterized by bloating, abdominal pain, and changes in stool frequency and/or consistency. For many patients, IBS-related symptoms are not alleviated by the current treatments available. Some evidence suggests that changes in the bowel microbiota of patients with IBS may play a role in the pathophysiology. Systemic antibiotics have shown inconsistent results for symptomatic relief in patients with IBS, but a nonsystemic antibiotic, such as rifaximin (Xifaxan), could allow a targeted therapy for reduction or alleviation of IBS symptoms. Pimentel and colleagues investigated rifaximin as an effective treatment for the alleviation of bloating, abdominal pain, and loose stools in patients who had IBS without constipation.

The Study: The authors evaluated two randomized placebo-controlled trials (TARGET 1 and TARGET 2) of patients who had IBS without constipation. Patients were randomized to receive 550 mg of rifaximin or placebo three times per day for two weeks. Symptoms were recorded for an additional 10 weeks after treatment ended. Study end points were the percentage of patients with adequate relief (for at least two of the first four weeks after treatment) of global IBS symptoms, bloating, abdominal pain, and loose stools. Patients were asked to rate the average daily amounts of abdominal pain and bloating, and the average daily stool consistency.

Results: In both trials, significantly more patients in the rifaximin group (40.7 versus 31.7 percent in the placebo group) experienced adequate relief of global IBS symptoms during the first month after treatment. Significantly more patients treated with rifaximin self-reported adequate relief of bloating in both trials (40.2 versus 30.3 percent for placebo). In addition, patients receiving rifaximin self-reported significant improvement in abdominal pain and stool consistency compared with placebo. There were no significant differences in the rates of infections or other adverse events between groups.

Conclusion: Patients who have IBS without constipation experience significant relief of global IBS symptoms, abdominal pain, bloating, and loose stools after two weeks of treatment with 550 mg of oral rifaximin, three times per day.