Development of drugs for gastrointestinal motor disorders: Translating science to clinical need

Only a small number of new drugs have recently become available for gastrointestinal (GI) disorders. This is partly because we await outcomes of research into functional bowel disorder aetiology (e.g., role of microbiota) and of trials to control stress- related or painful GI symptoms (e.g., via CRF ₁ receptors or β₃ adrenoceptors). Nevertheless, only the ClC-2 channel activator lubiprostone has recently reached the clinic, joining the 5-HT₃ antagonist alosetron and the long-established 5-HT₄ agonist and D₂ antagonist metoclopramide; tegaserod, a non-selective ligand, was withdrawn. Interestingly, each has shortcomings, providing opportunities for molecules with 5-HT₄ or motilin receptor selectivity, and for new biology via guanylate cyclase C or ghrelin receptor activation. For translation into new drugs, the molecule must have appropriate efficacy, selectivity and pharmacodynamic properties. It is argued that the compound must then be evaluated in conditions where changes in motility are known to exist, before considering more difficult symptomatic conditions such as irritable bowel syndrome (IBS) or functional dyspepsia (FD), where relationships with disordered motility are unclear. Thus, it may be better to begin studying a gastric prokinetic in diabetics requiring improved glucose control, rather than in FD. Notably, new 5-HT₄ receptor agonists are being evaluated firstly as treatments of constipation, not IBS. New antidiarrhoeal agents should be developed similarly. Thus, progression of new drugs may require initial studies in smaller patient populations where clinical outcome is better defined. Only then can disease-related ideas be properly tested and drugs brought forward for these disorders (with high clinical need) and then, if successful for IBS and FD.