Nausea and the quest for the perfect anti-emetic.

The discovery of anti-emetic agents is reviewed to illustrate the large database (>129,000 papers in PubMed) available for potential data mining and to provide a background to the shift in interest to nausea from vomiting. Research on nausea extends to identification of biomarkers for diagnosis/clinical trials and to understanding why nausea is such a common dose-limiting toxicity of diverse therapeutic agents. The lessons learned for translation from animals to humans, from the discovery of the anti-vomiting effects of 5-HT3 and NK1 receptor antagonists, is discussed in terms of the similarities between the emetic pathways and their pharmacology, and also in terms of the limitations of rodent models of "nausea" (pica, conditioned taste aversion, conditioned gaping and disgust). The review focuses on the established view that anti-emetics are more efficacious against vomiting than nausea. In particular we examine studies of 5-HT3, NK1 and D2 receptor antagonists, gabapentin and various receptor agonists. The potential for targeting anti-nausea agents is then considered, by targeting mechanisms which correct delayed gastric emptying (prokinetics), the rise in plasma vasopressin (AVP) and/or act at central targets revealed by the growing knowledge of cortical regions activated/inhibited in subjects reporting nausea. Modulation of the projections from the brainstem to the cortical areas responsible for the genesis of the sensation of nausea provides the most likely approach to a target at which an anti-nausea drug could be targeted with the expectation that it would affect nausea from multiple causes.