ONDANSETRON - A SEROTONIN RECEPTOR (5-HT3) ANTAGONIST FOR ANTINEOPLASTIC CHEMOTHERAPY-INDUCED NAUSEA AND VOMITING

Ondansetron represents a new class of drugs that exert their antiemetic activity by selective inhibition of a serotonin receptor subtype (5-HT3). Ondansetron has marked activity against emesis associated with cisplatin and other highly emetogenic drugs. Compared with high doses of metoclopramide, the antiemetic "gold standard", it demonstrates equal or superior efficacy. Although ondansetron is moderately well absorbed after oral administration, only a parenteral formulation will initially be available. Ondansetron is eliminated almost entirely by hepatic metabolism; less than five percent of an intravenously administered dose is recovered intact in urine. The half-life of ondansetron is approximately 3.5 hours; slightly shorter in children and prolonged in the elderly. Neither clinical efficacy nor adverse effects have correlated with serum concentrations. Ondansetron is generally well tolerated. Clinically relevant adverse effects include headache, diarrhea or constipation, sedation, and transient minor elevations of liver function tests. It is not associated with extrapyramidal reactions. Ondansetron is indicated as prophylaxis for nausea and vomiting associated with emetogenic chemotherapy. Studies to further evaluate and define its use are ongoing.