Antiemetics - D2 antagonists Flashcards
What are common indications for using dopamine antagonist anti-emetics?
Prophylaxis and treatment of nausea and vomiting - particularly in context of reduced gut motility
What are exxample of D2-antagonist anti-emetics?
- Metoclopramide
- Domperidone
D2-receptors are the main receptor in which part of the vomiting pathway/system?
CTZ
What is the CTZ responsible for?
Sensing emetogenic substances in the blood (e.g. drugs)
How do D2 antagonist anti-emetics work?
Block D2 receptors in the CTZ and the gut. Blockade of gut receptors has a prokinetic effect, promoting gastric emptying and enhancing anti-emetic effect
What is the role of dopamine in the gut?
Dopamine is an important neurotransmitter in the gut, where it promotes relaxation of the stomach and lower oesophageal sphincter and inhibits gastroduodenal coordination
What causes of nausea and vomiting are D2-antagonists particularly useful for treating?
- CTZ stimulation by drugs
- Causes of reduced gut motility - Opiods, diabetic gastroparesis
What are important side effects of D2-antagonist anti-emetics?
- Diarrhoea
-
Extrapyramidal syndromes
- Acute dystonic reaction - oculogyric crisis
When are D2-antagonists contraindicated?
Particularly metoclopramide
- GI obstruction
- Perforation
- GI hemorrhage - haematemesis/malaena
What drugs can D2-antagonists interact with?
- Antipsychotics
- Dopaminergic agents for parkinson’s
Why does domperidone not tend to cause extrapyramidal side effects unlike metoclopramide?
It does not cross the blood brain barrier
What dose of domperidone might you start someone on?
10mg up to 3 times daily for up to 1 week
How can metoclopramide be administered?
- Oral
- IV
What dose of metoclopramide can you start someone on for nausea and vomiting?
10 mg up to 3 times daily for up to 5 days
How quickly should 10 mg metoclopramide be given if administered IV?
Over 2 minutes
