GI Pharmacology — Metoclopramide

Current · V5 (2025) → J4.ii Historical · V4 (2023) → O2.ii 1 exam appearance

2012A Q23

Exam question

Classify antiemetic drugs and give an example from each group (60% of marks). Outline the gastrointestinal effects of metoclopramide (40% of marks).

CICMWrecks answer

Master answer

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

Selective stimulation of gastric muscarinic receptors
- acts primarily by augmenting release of ACh and perhaps by inhibition of 5-HT release
- Coordinated gastric, pyloric and duodenal activity contraction (accelerates gastric emptying)
- Increased amplitude and frequency of Longitudinal muscle contraction
- Lowers threshold for peristaltic reflex to occur
Reduces intestinal muscle fatigue
Direct action on smooth muscle to increase tone (including increased LOS)
relaxes the pyloric sphincter

Past papers

1 appearance

Exam	Exact exam wording	Candidate success
2012A Q23	Classify antiemetic drugs and give an example from each group (60% of marks). Outline the gastrointestinal effects of metoclopramide (40% of marks).	40%