FDA and EMA end points: which outcome end points should we use in clinical trials in patients with irritable bowel syndrome?

Trial design and endpoints for the evaluation of drug efficacy in irritable bowel syndrome (IBS) underwent major changes over the last two decades. A systematic review in the early 1990s concluded that there were few well-designed and well-executed treatment trials in IBS. Over the next decade, the so-called binary endpoints were used in several clinical trials in IBS in the US, Europe and other parts of the world. In 2006, the Food and Drug Administration (FDA) published a general guidance for the evaluation of symptom benefit in clinical trials based on patient-reported outcome (PRO) measures, which had a major impact on trial design in IBS. In May 2012, the FDA recommended to use as provisional endpoint the quantification of two major IBS aspects, abdominal pain and disordered defecation, to assess the efficacy of pharmacological treatments in IBS. In the present issue of Neurogastroenterology & Motility, the performance of the FDA Responder Endpoint for clinical trials in irritable bowel syndrome with constipation was evaluated using data from two large Phase III clinical trials of linaclotide. The FDA interim endpoints are clinically relevant as they are also able to capture the smallest patient-reported difference in the domain of Abdominal Pain intensity and Abnormal Defecation with good diagnostic accuracy. The FDA responder definition and the European Medicines Agency responder definitions generate similar response rates, while binary endpoints generate higher responder rates. The implications for optimalization and harmonisation are discussed.