A drug used to prevent nausea and vomiting caused by chemotherapy. It is also used to prevent nausea and vomiting after surgery. Palonosetron hydrochloride blocks the action of the chemical serotonin, which binds to certain nerves and may trigger nausea and vomiting. Blocking serotonin may help lessen nausea and vomiting. Palonosetron hydrochloride is a type of serotonin receptor antagonist and a type of antiemetic. Also called Aloxi.