Canonical Question

GIT Pharm – Gastric fluid

V5 J4.ii Historical V4 O2.ii 2 appearances

Master answer

Anti-emetic Agents

CLASSEXAMPLESMECHANISM OF ACTION
AnticholinergicsHyoscine
Atropine		– M1-Ach-R antagonism (NTS, CTZ, VC)
– Small antihistamine and D2 antagonist effects
Antihistamines (H1)Cyclizine
Promethazine		– H1 antagonism- VC, vestibular nucleus and CTZ
– Anti-muscarinic effects- NTS, CTZ, vomit center
– D2 antagonism (GIT, CTZ)
5-HT3 AntagonistsOndansetron– Peripheral in GIT
– Central at VC and CTZ
Dopamine Antagonists1. Phenothiazines
– Prochlorperazine (stemetil)
2. Butyrophenones
– Droperidol, domperidone
3. Benzamides
– Metoclopramide		– Decreased sensitivity of visceral afferents to vomit center
– Central D2 blockade increased threshold at CTZ

Other effects:
– Inhibition of 5-HT3
– Anti-H1 effects
SteroidsDexamethasone– Proposed to act centrally to inhibit prostaglandin synthesis and inhibit endorphin receptors
Miscellaneous1. Propofol
2. Benzos
3. Cannabinoids
4. NK1- Receptor antagonists (aprepitant)		– Propofol and BZD- GABAergic inhibition of VC
– Cannabinoids- Direct CTZ and VC inhibition
– NK1 antagonists inhibit VC

Exam appearances

ExamExact wordingRelationshipSuccess
2009B Q14 Classify antiemetic drugs and describe their mechanism of action. historical_member —
2016A Q23 Classify anti-emetic agents by describing their mechanism of action and provide examples. historical_member —