Aprepitant-d4 is a labeled analogue of Aprepitant (A729800), A novel selective neurokinin-1 (NK-1) receptor antagonist. In vitro studies using human liver microsomes indicate that Aprepitant is metabolised primarily by CYP3A4 with minor metabolism by CYP1A2 and CYP2C19, and no metabolism by CYP2D6, CYP2C9, or CYP2E1. Aprepitant-d4 is a potential treatment for chemotherapy induced nausea and vomiting.