Small Intestinal Bacterial Overgrowth: Novel Insight in the Pathogenesis and Treatment of Irritable Bowel Syndrome

Abstract

A total of 65-84% of patients with irritable bowel syndrome (IBS) presents with small intestinal bacterial overgrowth (SIBO). SIBO is defined as the presence of more than 105 cfu/ml of colonic type bacteria in the lumen of the small bowel. It is more common in patients with IBS and predominant bloating and diarrhea. Based on the implication of SIBO in the pathogenesis of IBS, six trials have been conducted and analyzed in this review aiming to define a role of rifaximin for the management of IBS. Rifaximin is an orally administered antimicrobial with limited systemic absorption and considerable potency against bacteria implicated in SIBO. In two trials patients with SIBO irrespective of the presence of IBS were enrolled. A positive effect of rifaximin was denoted in the eradication of SIBO in both.One double-blind, prospective randomized trial over placebo in patients with IBS denoted a substantial improvement of the global assessment of patients after treatment with rifaximin. Benefit remained for 10 weeks after stop of treatment. A major benefit was disclosed for bloating. Another three prospective randomized trials have been conducted in patients with both IBS and SIBO. Rifaximin significantly eradicated SIBO and improved bloating.These findings led the Task Force for IBS of the American College of Gastroenterology to appoint a grade of evidence of 1B for the administration of rifaximin in the management of IBS. The proposed oral regimen is 400 mg three times daily for 10 days. However, results of large Phase III trials are mandatory.