Casopitant mesylate (GW679769B) is a selective, brain permeable, and orally active antagonist of neurokinin 1 (NK1) receptor. It is a second in the class of antiemetics.

In a ferret-model of Cisplatin-induced emesis, Casopitant inhibits retching and vomiting and reduced nausea-like behaviours in a dose-dependent manner. Following a single intraperitoneal dose, radioactive labeled Casopitant ([14C]Casopitant) is rapidly absorbed, with plasma and brain concentrations being approximately equal at two hours post-dosing. [14C]Casopitant is found in the brain as the parent compound and two major oxidative metabolites (M1 and M2), accounting for approximately 76%, 19%, and 3% of the radioactivity, respectively. Casopitant possesses a high affinity for brain NK1 receptors in the ferret [2].