Irritable bowel syndrome clinical trial design: future needs.

This article addresses a series of points that should be considered in the design of future clinical trials in irritable bowel syndrome (IBS). A precise, uncontroversial definition of the disorder and the affected patient is required that accurately describes the condition that practitioners recognize intuitively exists. Regarding patient source and selection, the principle should be applied that patients be recruited to trials from all sources to which an indication is intended. Because abdominal pain is the most central symptom of IBS, it should be used as the primary trial endpoint. Because there are currently no effective treatments, placebo-controlled trials pose no ethical problems. High placebo responses may equally well be the temporary spontaneous improvements that are characteristic of the condition. Clinical trials should be designed to meet specific aims of treatments: when taken as single doses to terminate an attack of pain; when taken over a brief period of time to speed resolution of a period of exacerbation of IBS; when taken after termination of a period of activity to prevent relapse; when taken regularly on a long-term basis to reduce the days on which a number of symptoms are experienced; when taken in form of discrete courses of treatment designed to achieve a pivotal change in the natural history of the condition.