[Ondansetron: a specific 5-HT3 serotonin receptor inhibitor, a new antiemetic in oncology].

Serotonin (5-Hydroxytryptamine) seems to play a dominant role in triggering vomiting induced by cytotoxic agents through the stimulation of 5-HT3 receptors. They have been observed in the GI tract as well as in the brain (area postrema). Ondansetron is a specific antagonist of 5-HT3 serotonin receptors. Its anti-emetic activity is very powerful in the ferret. The availability of an injectable or oral form of this product allows the overall treatment of acute and delayed emesis and its administration is in accordance with different schedules: single IV injection or a continuous 24 hour infusion or repeated IV injection followed by oral treatment. The pharmacokinetics of the drug are as follows: absorption begins about 30 minutes after the administration per os, its biodisponibility is about 60%, its clearance: 20 ml/minute and its elimination half life about 3 hours. Different double blind studies, carried out in parallel groups or in cross over, demonstrated the superiority of ondansetron over metoclopramide in the control of nausea and vomiting, whether or not the chemotherapy contained cisplatin; a more recent study shows also that ondansetron was superior to alizapride and methylprednisolone in combination. Side effects of ondansetron do not include extrapyramidal symptoms but only headaches and constipation. The use of ondansetron improves the well-being of patients receiving chemotherapy and increases protocol compliance.