GI: ANTIEMETICS - DOPAMINE D2 RECEPTOR ANTAGONISTS

Question 1

D2 RECEPTOR ANTAGONISTS: INDICATIONS

Answer 1

• Nausea and vomiting in the context of reduced gut motility

Question 2

D2 RECEPTOR ANTAGONISTS: MOA

Answer 2

• Nausea and vomiting are triggered by a variety of factors + stimuli
• Various pathways converge on the VOMITING CENTRE in the Medulla (receives inputs from the CHEMORECEPTOR TRIGGER ZONE, STN, VESTIBULAR SYSTEM + HIGHER NEUROLOGICAL CENTRES
• Dopamine, via D2 receptors = main receptor in CTZ which is responsible for sensing emetogenic substances in the blood (eg drugs)
• D also promotes relaxation of the stomach and LOS -> inhibiting gastroduodenal coordination
• D2 receptor Antagonists = PROKINETIC EFFECT = promote gastric emptying (contributes to antiemetic effect)
• CTZ stimulation = effective in nausea and vomiting and reduced gut motility

Question 3

D2 RECEPTOR ANTAGONISTS: IMPORTANT ADVERSE EFFECTS

Answer 3

• Diarrhoea
• Metoclopramide can induce EXTRAPYRAMIDAL SYNDROMES via same mechanism as antipsychotics
• Most likely to take the form of an acute dystonic reaction such as OLIGYRIC REACTION
• Domperidone tends not to cause extrapyramidal symptoms as it does not cross the BBB

Question 4

D2 RECEPTOR ANTAGONISTS: CONTRAINDICATIONS

Answer 4

• Extrapyramidal side effects are more common in children and young adults
• GI obstruction
• Perforation

Question 5

D2 RECEPTOR ANTAGONISTS: INTERACTIONS

Answer 5

• Extrapyramidal SEs increased with antipsychotics

- DO NOT COMBINE with Dopaminergic agents for Parkinsons Dx

Question 6

D2 RECEPTOR ANTAGONISTS: EXAMPLES

Answer 6

• Metoclopramide

- Domperidone