Bacteria and the Role of Antibiotics in Irritable Bowel Syndrome

INTRODUCTION Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by symptoms, such as abdominal pain, bloating, diarrhea, and constipation, that are not attributable to structural or biochemical abnormalities (1). Although several conceptual models of IBS pathogenesis have been suggested, including visceral hypersensitivity, abnormal intestinal motility, immune activation, and altered brain-gut interactions, none fully explain the heterogeneous range of symptoms associated with IBS (1,2). Emerging evidence suggests that bacteria, specifically small intestinal bacterial overgrowth (SIBO), may be involved in producing some IBS symptoms (3,4). These findings provide a rationale for the potential therapeutic benefit of antibiotic therapy. This article Mark Pimentel, M.D., F.R.C.P.(C), Director, GI Motility Program, Cedars-Sinai Medical Center and UCLA Geffen School of Medicine, Los Angeles, CA. Although several pathophysiologic models have been suggested, the etiology of irritable bowel syndrome (IBS) is unknown. Emerging evidence suggests that small intestinal bacterial overgrowth (SIBO) may explain some symptoms associated with IBS. The putative contribution of bacteria to IBS pathophysiology and symptoms provides a rationale for investigating the efficacy and safety of antibiotics in IBS. Although few controlled studies have been conducted, evidence has suggested that antibiotics may reduce the presence of SIBO and improve symptoms of IBS. Several antibiotics, including rifaximin and neomycin, have been shown to effectively reduce bacterial overgrowth and improve bowel symptoms in patients with SIBO and/or IBS. Rifaximin may be well suited for the treatment of IBS due to its favorable safety profile. Further research is warranted to more fully elucidate the role of bacteria in IBS and the therapeutic benefits of antibiotics in the treatment of IBS.