Emerging pharmacological therapies for the irritable bowel syndrome.

The irritable bowel syndrome (IBS) is a symptom-based disorder defined by the presence of abdominal pain and altered bowel habits. Clinical presentations of IBS are diverse, with some patients reporting diarrhea, some constipation, and others a mixture of both. Like the varied clinical phenotypes, the pathogenesis of IBS is also diverse. IBS is not a single disease entity, but rather likely consists of several different disease states. This fact has important implications for the choices and efficacy of IBS treatment. This article reviews the IBS drugs that have reached phase II or III clinical trials.