Background
Evidence suggests that gut flora may play an important role in the pathophysiology
of the irritable bowel syndrome (IBS). We evaluated rifaximin, a minimally absorbed
antibiotic, as treatment for IBS.
Methods
In two identically designed, phase 3, double-blind, placebo-controlled trials
(TARGET 1 and TARGET 2), patients who had IBS without constipation were randomly
assigned to either rifaximin at a dose of 550 mg or placebo, three times
daily for 2 weeks, and were followed for an additional 10 weeks. The primary end
point, the proportion of patients who had adequate relief of global IBS symptoms,
and the key secondary end point, the proportion of patients who had adequate relief
of IBS-related bloating, were assessed weekly. Adequate relief was defined as selfreported
relief of symptoms for at least 2 of the first 4 weeks after treatment.
Other secondary end points included the percentage of patients who had a response
to treatment as assessed by daily self-ratings of global IBS symptoms and individual
symptoms of bloating, abdominal pain, and stool consistency during the 4 weeks
after treatment and during the entire 3 months of the study.
Results
Significantly more patients in the rifaximin group than in the placebo group had
adequate relief of global IBS symptoms during the first 4 weeks after treatment
(40.8% vs. 31.2%, P = 0.01, in TARGET 1; 40.6% vs. 32.2%, P = 0.03, in TARGET 2;
40.7% vs. 31.7%, P<0.001, in the two studies combined). Similarly, more patients in
the rifaximin group than in the placebo group had adequate relief of bloating
(39.5% vs. 28.7%, P = 0.005, in TARGET 1; 41.0% vs. 31.9%, P = 0.02, in TARGET 2;
40.2% vs. 30.3%, P<0.001, in the two studies combined). In addition, significantly
more patients in the rifaximin group had a response to treatment as assessed by
daily ratings of IBS symptoms, bloating, abdominal pain, and stool consistency.
The incidence of adverse events was similar in the two groups.
Conclusions
Among patients who had IBS without constipation, treatment with rifaximin for
2 weeks provided significant relief of IBS symptoms, bloating, abdominal pain, and
loose or watery stools.