Aprepitant is an antiemetic chemical compound that belongs to a class of drugs called substance p antagonists (spa). it mediates its effect by blocking the neurokinin 1 (nk1) receptor.aprepitant is used for:preventing nausea and vomiting caused by certain types of cancer medicines (chemotherapy). it is used in combination with other medicines. it is also used to prevent nausea and vomiting after surgery.