The hydrochloride salt of the racemic form of ondansetron, a carbazole derivative and a selective, competitive serotonin 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist with antiemetic activity. Although its mechanism of action has not been fully characterized, ondansetron appears to competitively block the action of serotonin at 5HT3 receptors peripherally in the gastrointestinal tract as well as centrally in the area postrema of the CNS, where the chemoreceptor trigger zone (CTZ) for vomiting is located, resulting in the suppression of chemotherapy- and radiotherapy-induced nausea and vomiting. Check foractive clinical trials using this agent. or A drug used to treat acute myelogenous leukemia (AML). It is also being studied in the treatment of several other types of cancer. It blocks cell growth by damaging the cell’s DNA and may kill cancer cells. It is a type of alkylating agent. Also called Cloretazine and laromustine.