A potent NK1 receptor antagonist (Ki = 0.66 nM for the human receptor); greater than 1,000-fold selective for NK1 over NK2 and NK3 and lacks activity in a panel of 100 receptors, transporters, enzymes, and ion channels; prevents apomorphine- and cisplatin-induced emesis in ferrets (ED50s = 0.03 and 0.07 mg/kg, respectively)