People are cautioned to seek immediate medical care if symptoms such as irregular heartbeat/palpitations, shortness of breath, dizziness, or fainting occur while taking ondansetron. Overdose
No specific treatment is available for ondansetron overdose; people are managed with supportive measures. An antidote to ondansetron is not known. Pharmacology
Pharmacodynamics
Ondansetron is a highly selective serotonin 5-HT3 receptor antagonist, with low affinity for dopamine receptors. The 5-HT3 receptors are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema in the medulla. Serotonin is released by the enterochromaffin cells of the small intestine in response to chemotherapeutic agents and may stimulate vagal afferents (via 5-HT3 receptors) to initiate the vomiting reflex. It is thought that ondansetrons antiemetic action is mediated mostly via antagonism of vagal afferents with a minor contribution from antagonism of central receptors. Pharmacokinetics
Ondansetron may have a degree of peripheral selectivity due to binding to P-glycoprotein and efflux out of the brain at the blood–brain barrier. History
Ondansetron (marketed under the brand name Zofran) was developed in the mid-1980s by GlaxoSmithKline in London. It was granted US patent protection in September 1987, received a use patent June 1988, and was approved by the US FDA in January 1991. It was granted another divisional patent in November 1996. Finally, owing to GlaxoSmithKlines research on pediatric use, ondansetrons patent protection was extended until December 2006.
It is typically used after other antinausea drugs have failed.There appears to be a low risk of harm to the baby with use during pregnancy, though there may be an increase in heart problems among the babies.Ondansetron is in pregnancy category B in the US. It is not known if ondansetron is excreted in breast milk. Cyclic vomiting syndrome
Ondansetron is one of several antiemetic drugs used during the vomiting phase of cyclic vomiting syndrome. Gastroenteritis
Trials in emergency department settings support the use of ondansetron to reduce vomiting associated with gastroenteritis and dehydration. A retrospective review found it was used commonly for this purpose, being administered in over 58% of cases. Its use reduced hospital admissions, but was also associated with higher rates of return visits to the emergency department. Furthermore, people who had initially received ondansetron were more likely to be admitted on the return visit than people who had not received the drug. However, this effect may simply be due to the agent being used more frequently in people who present with more severe illness. Its use was not found to mask serious diagnoses. Special populations
Children
Ondansetron has rarely been studied in people under 4 years of age. As such, little data is available to guide dosage recommendations. Elderly
It is not necessary to adjust the dosage for people under 75 years of age. The use of ondansetron has not been studied in people older than 75 years of age, and it is not known if dosage should be adjusted for this group.