Purpose of review: Few therapies are of proven efficacy in irritable bowel syndrome. Thus, there is great interest in the development of a natural therapy that can be both safe and effective. An understanding that probiotics are heterogeneous, with multiple targets and mechanisms of action, is fundamental to the development of clinical trials.
Recent findings: A bidirectional model for the pathogenesis of irritable bowel syndrome is proposed in which gut-driven and brain-driven mechanisms contribute to the genesis of gut dysfunction and symptoms. In-vitro and animal studies have generated most of the mechanistic rationale for the use of probiotics in functional bowel disorders. A MEDLINE search of publications from 1989 to date revealed only eight placebo-controlled clinical trials on the subject of probiotics and irritable bowel syndrome. All these studies suffer from methodologic problems. By contrast, numerous reviews have been published in the past 2 years on this subject.
Summary: Animal research will continue to identify novel targets and elucidate the mechanisms of action of probiotics, thus providing a rational basis for their use in irritable bowel syndrome. The notion of treating irritable bowel syndrome with probiotics is particularly attractive to patients and generates great interest, although clinical evidence is not yet sufficient to enable clear guidelines to be designed. Large, well-designed, controlled clinical trials using specific probiotics are warranted.