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Indications

Ondansetron is a serotonin subtype 3 (5-HT3) receptor antagonist indicated:
  • Prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy.
  • Prevention and treatment of post-operative nausea and vomiting.
  • Prevention of radiotherapy-induced nausea and vomiting.

Pharmacology

Ondansetron is a potent, highly selective 5HT3 receptor-antagonist. Its precise mode of action in the control of nausea and vomiting is not known. Chemotherapeutic agents and radiotherapy may cause release of 5HT in the small intestine initiating a vomiting reflex by activating vagal afferents via 5HT3 receptors. Ondansetron blocks the initiation of this reflex. Activation of vagal afferents may also cause a release of 5HT in the area postrema, located on the floor of the fourth ventricle, and this may also promote emesis through a central mechanism. Thus, the effect of ondansetron in the management of the nausea and vomiting induced by cytotoxic chemotherapy and radiotherapy is probably due to antagonism of 5HT3 receptors on neurons located both in the peripheral and central nervous system. The mechanisms of action in post-operative nausea and vomiting are not known but there may be common pathways with cytotoxic induced nausea and vomiting.

Dosage & Administration

Chemotherapy-Induced Nausea and Vomiting-

Adults, Pediatric patients (6 months to 18 years):
  • 8 mg tablet/orodispersible tablet: Three 0.15 mg/kg doses, up to a maximum of 16 mg per dose.
  • 4 mg orodispersible tablet: Three 0.15 mg/kg doses, up to a maximum of 16 mg per dose.
  • Injection: Three 0.15 mg/kg doses, up to a maximum of 16 mg per dose, infused intravenously over 15 minutes.

Radiotherapy-Induced Nausea and Vomiting-

Adults:
  • 8 mg tablet/orodispersible tablet: Initial Dose: 8 mg orally 1 to 2 hours before radiotherapy. Post Radiotherapy: 8 mg orally every 8 hours for up to 5 days after a course of treatment.
  • 4 mg orodispersible tablet: Three 0.15 mg/kg doses, up to a maximum of 16 mg per dose.
  • Injection: Three 0.15 mg/kg doses, up to a maximum of 16 mg per dose, infused intravenously over 15 minutes.


Postoperative Nausea and Vomiting-

Adults:
  • 8 mg tablet/orodispersible tablet: 16 mg given as two 8 mg tablets
  • 4 mg orodispersible tablet: 16 mg
  • Injection: 4 mg
Pediatrics (>40 kg): Injection: 4 mg
Pediatrics (40 kg): Injection: 0.1 mg/kg

Interaction

The potential for clinically significant drug interactions with Ondansetron appears to be low.

Contraindications

Contraindicated in patients known to have hypersensitivity to the drug or any of its components. Concomitant use of apomorphine.

Side Effects

The most common adverse reactions in chemotherapy-induced nausea and vomiting (incidence 7%) are diarrhea, headache and fever. The most common adverse reactions in postoperative nausea and vomiting in adults is headache (incidence 10%), and in pediatric patients aged 1 to 24 months is diarrhea (incidence 2%).

Pregnancy & Lactation

Pregnancy Category B. Ondansetron is excreted in the breast milk of rats. It is not known whether ondansetron is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when ondansetron is administered to a nursing woman.

Precautions & Warnings

Hypersensitivity reactions, including anaphylaxis and bronchospasm, have been reported with or without known hypersensitivity to other selective 5-HT3 receptor antagonists. QT prolongation occurs in a dose-dependent manner.

Use in Special Populations

Geriatric Use: Dosage adjustment is not needed in patients over the age of 65.
Hepatic Impairment: A total daily dose of 8mg should not be exceeded (patients with severe hepatic impairment).
Renal Impairment: No dosage adjustment is recommended.

Therapeutic Class

Anti-emetic drugs

Storage Conditions

Store at temperature not exceeding 30ºC in a dry place. Protect from light and moisture.