Past Papers · SAQ
GI Pharmacology — Antiemetic Classification
2016A Q23
Exam questionClassify anti-emetic agents by describing their mechanism of action and provide examples.
CICMWrecks answer
Master answer
Anti-emetic Agents
| CLASS | EXAMPLES | MECHANISM OF ACTION |
|---|---|---|
| Anticholinergics | Hyoscine 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 Antagonists | Ondansetron | – Peripheral in GIT – Central at VC and CTZ |
| Dopamine Antagonists | 1. 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 |
| Steroids | Dexamethasone | – Proposed to act centrally to inhibit prostaglandin synthesis and inhibit endorphin receptors |
| Miscellaneous | 1. 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 |
Past papers