Ondansetron hydrochloride dihydrate (GR 38032, SN 307) is a potent, highly selective 5-HT3 receptor antagonist with IC50 of 103 pM. Ondansetron shows negligible agonist or antagonist activity on other 5-HT or non-5-HT receptor-containing tissues. Ondansetron antagonizes the bradycardic response to 5-HT or 2-methyl-5-HT administered intravenously (i.v.) to anaesthetized animals.
