Antiemetics - serotonin 5HT3 antagonists

Question 1

What are indications for 5-HT3 inhibitors?

Answer 1

Nausea and vomiting - general anaeasthesia and chemotherapy

Question 2

What is the mechanism of action of 5-HT3 antagonists?

Answer 2

• Block 5-HT3 receptors in the CTZ - senses emetogenic substances in the blood (e.g. drugs)
• Block 5-HT3 receptors in the gut - Blocks serotonin release by the gut in response to emetogenic stimuli. This blocks action of serotonin on the vagus nerve, which in turn blocks activation of the vomiting centre via the solitary tract nucleus.

Question 3

What types of nausea and vomiting are 5-HT3 antagonists effective against?

Answer 3

• Drugs
• Visceral stimuli (gut infection, radiotherapy)

Question 4

What cause of nausea and vomiting are 5-HT3 antagonists not good at treating?

Answer 4

Motion sickness

Question 5

What are adverse effects of 5-HT3 antagonists?

Answer 5

Rare, but

• Constipation
• Diarrhoea
• Headaches
• Serotonin syndrome

Question 6

When should 5-HT3 antagonists not be given?

Answer 6

Those with prolonged QT

Question 7

What are examples of 5-HT3 antagonists?

Answer 7

Ondansetron