Treatment of nausea and vomiting: gaps in our knowledge.

The past 20 years have seen notable advances in our understanding of the physiology and pharmacology of the emetic reflex leading to the identification of the anti-emetic effects of 5-hydroxytryptamine(3) (5-HT(3)) and neurokinin(1) receptor (NK(1)) antagonists. The introduction of 5-HT(3) and NK(1) receptor antagonists into the clinic has had a major impact in alleviating the nausea and vomiting associated with the treatment of cancer and the sequelae to anaesthesia and surgery (post-operative nausea and vomiting, PONV). Despite these advances there are major gaps in our understanding. Interestingly, one of these is the relatively poor ability to treat nausea. Additional gaps in our knowledge are highlighted to provide a framework within which directions for research can be proposed. Particular attention is drawn to: lacunae in knowledge of some currently used anti-emetics such as the source of dopamine required to initiate emesis; the theoretical assumptions and mechanisms underlying the concept of a "universal anti-emetic"; the variety of receptors at which agonists act to have anti-emetic effects (GABA (B), CB(1), 5-HT(1A), ghrelin, opioid); issues of translation from animals to humans and the relationship between the pathways involved in emesis and certain gastrointestinal disorders such as dyspepsia and gastroesophageal reflux, with the latter being of particular interest as some agents affecting reflux are also anti-emetic. Together, the unmet clinical need to adequately control nausea, possibly by new drugs acting within the brainstem, and the significant gaps in understanding key aspects of the emetic reflex, suggest an important need to focus and re-direct research into the distressing and sometimes life-threatening symptoms of nausea and vomiting.