An antibiotic therapy is the first potential drug treatment to offer symptom relief in irritable bowel syndrome (IBS) even after the medication is discontinued, according to investigators.

Rifaximin—an oral, nonsystemic, broad-spectrum antibiotic—targets the gut and is associated with a low risk of bacterial resistance. It is FDA-approved for the treatment of travelers’ diarrhea and hepatic encephalopathy and is available as Xifaxan through Salix Pharmaceuticals, which funded this research.

In two trials involving 1,260 persons who had IBS without constipation, significantly more patients using rifaximin 550 mg t.i.d. for 14 days had more adequate relief of global IBS symptoms, bloating, abdominal pain, and loose or watery stools than did placebo users. The relief lasted for up to 10 weeks after completion of therapy (N Engl J Med. 2011;364:22-32, accessed February 15, 2011).