Burapitant (SSR-240,600) is a drug developed by Sanofi-Aventis which was one of the first compounds developed that acts as a potent and selective antagonist for the NK1 receptor. Burapitant inhibited the binding of radioactive substance P to tachykinin NK1 receptors in human lymphoblastic IM9 cells, human astrocytoma U373MG cells, and human brain cortex. It also showed a subnanomolar affinity for guinea pig NK1 receptors but was less potent on rat and gerbil NK1 receptors. Burapitant inhibited [Sar(9),Met(O2)(11)]substance P-induced inositol monophosphate formation in human astrocytoma U373MG cells. Burapitant (0.1-10 mg/kg i.p. or p.o.) antagonized the excitatory effect of i.c.v. infusion of [Sar(9),Met(O2)(11)]substance P (SP) on the release of acetylcholine in the striatum of anesthetized and awake guinea pigs. This antagonistic action was still observed after repeated administration of Burapitant (5 days, 10 mg/kg p.o., once a day). Burapitant (10 mg/kg i.p.) inhibited the phosphorylation of the cAMP response element-binding protein in various brain regions induced by i.c.v. administration of [Sar9,Met(O2)(11)]SP. While burapitant itself did not proceed beyond early clinical trials and was never developed for clinical use in humans, promising animal results from this and related compounds have led to a number of novel drugs from this class that has now been introduced into medical use.