Ondansetron

Question 1

What type of medication is Ondansetron?

Answer 1

An anti-emetic and anti-nauseant.

Question 2

What is the mechanism of action of Ondansetron?

Answer 2

Ondansetron antagonises Seratonin 5-HT3 receptors both centrally (vomiting center(1) ) and peripherally (vagus nerve terminals) to prevent nausea. The peripheral effects are the primary source of the antiemetic effects as within the GI tract, the vagus nerve senses nausea and vomiting triggers. Ondansetron is metabolised primarily by the cytochrome P450 system of the liver(2).

(1) This is located in the area postrema in the chemoreceptor trigger zone.
(2) Enzymes, located mainly in the liver, that synthesise (form) and metabolise (break down) various chemicals and molecules within the body.

Question 3

What is the route, onset, peak and duration of Ondansetron?

Answer 3

• IM
  
  • Onset: 10-15min
  • Peak: N/A
  • Duration: 1-2hrs
• IV
  
  • Onset: 3-5min
  • Peak: N/A
  • Duration: 1-2hrs
• Notes:
  
  • Slow IV administration is the preferred route.
  • IM should only be used when IV access is not available.

Question 4

What are the uses of ondansetron?

Answer 4

• Nausea & vomiting: Severe nausea and/or active vomiting.
• Eye injuries: Suspected penetrating eye injuries. (this is to prevent expulsion of ocular contents due to raised intraocular pressure from vomiting).

Question 5

What are the contraindications of ondansetron?

Answer 5

• Patients <2yrs of age
• Allergy/hypersensitivity to ondansetron
• Concurrent apomorphine administration

Question 6

What are the adverse effects of ondansetron?

Answer 6

• Headache and/or flushing
• Hypersensitivity reactions (including anaphylaxis)
• Seizures and movement disorders
• Visual disturbance

Question 7

What is the preparation and dosage of ondansetron?

Answer 7

• Preparation: 4mg (2ml) ampoule
• Dosage:
  
  • 2 - <8yo: 2mg bolus
    
    • Repeat: Nil
    • Max Total Dose: 2mg
  • 8+yo: 4mg bolus
    
    • Repeat: Nil
    • Max Total Dose: 4mg