Emerging drug for diarrhea predominant irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders with a 9 - 23% prevalence estimated in the general population. Patients can be subdivided into those who tend to have predominant diarrhea (IBS-D) or predominant constipation (IBS-C). Total annual productivity loss related to IBS in US is estimated at $205 million, with a significant impairment of health-related quality of life. A gold standard for the treatment of IBS is not established. Symptoms might improve with the use of few drugs and behavioral therapy, however, data concerning efficacy, safety and tolerability are limited. Therefore, development and validation of new therapies targeting at the molecular level are widely awaited.

We will specifically describe in this review Phase II and Phase III trials, with specific focus on treatment of IBS-D patients. Unfortunately, it is difficult to draw definite conclusions from Phase II and Phase III trials, because of the known high placebo effect.

Drugs active on opioid receptor subtypes and neurokinin (NK) receptors seem to be the most promising, but substantial progress of information in this field is still needed. The achievement of more insights on the pathogenesis of IBS could surely better drive and target the therapy, but still strong efforts are awaited.