GI: ANTIEMETICS - SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS

Question 1

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: INDICATIONS

Answer 1

• Prophylaxis and the Tx of nausea and vomiting - particularly in the context of Gen Anaesthesia and Chemo

Question 2

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: MOA

Answer 2

(Gut Irritation, Drugs, motion, vestibular disorders, stimuli) -> Inputs from CTZ, STN (innervated by VN), Vestibular System, Higher Neurological Centres -> Converge on Vom centre in the medulla

• Serotonin Fxns: Senses emetogenic substances in the blood (via high density of 5-HT3 receptors in CTZ) and Key NT in the gut (Stim of VN -> acts on the STN) -> triggers VOMITING CENTRE
• Antagonists act on the 5HT3 receptors and prevent stimulation ( Drugs and Visceral stimuli -> but not MOTION SICKNESS)

Question 3

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: ADVERSE EFFECTS

Answer 3

• Rare
• Diarrhoea
• Headaches
• Constipation

Question 4

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: WARNINGS

Answer 4

• Small risk of prolonging QT intervals, so should be avoided in these patients

Question 5

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: CONTRAINDICATIONS

Answer 5

• Drugs that prolong the Qt interval (Antipsychotics, Quinine, SSRIs)

Question 6

SEROTONIN 5-HT3 RECEPTOR ANTAGONISTS: EXAMPLES

Answer 6

• Ondansetron

- Granisesetron