Casopitant mesylate (GW679769B) is a potent, selective, brain permeable and orally active neurokinin 1 (NK1) receptor antagonist. Casopitant mesylate is a second in the class of antiemetics that acts to antagonise the emetogenic effect of substance P. Casopitant mesylate is also a substrate and a weak-to-moderate inhibitor of CYP3A4. Casopitant mesylate can be used for chemotherapy-induced nausea and vomiting (CINV) and postoperative nausea and vomiting (PONV).