2012A03 Classify the drugs which are useful for reducing the volume and acidity of gastric contents,
giving an outline of the mechanism of effect for each group.

Risk factors for aspiration injury

·  ↑Volume

·  ↑Acid

·  ↑Particulate matter

Physiology

Group

Drug

Mechanism of action

PPI

Omeprazole

·   Irreversibly inhibit H⁺K⁺ATPase

·   Most potent class

H2A

Ranitidine

·   ↓H_2R activity -> ↓G_s GPCR -> ↓cAMP -> ↓parietal cell activity

PGE1 analogue

Misoprostol

·   Binds PGE₂, PGE₃

·   ↑cAMP, Wnt pathway activation

Particulate antacid

Mg(OH)₄

Al(OH)₃

·   H⁺ + OH^- -> H₂O

·   More potent than non-particulate

Non-particulate antacid

Sodibic

·   H⁺ + HCO₃^- -> H₂O + CO₂

·   Less potent but lower risk pneumonitis if aspirated (cf. particulate)

Antimuscarinic

Atropine

Glycopyrrolate

·   Antagonists at m₁ and m₃ AChR

·   ↓IP₃ -> ↓ICF [Ca²⁺] (also ↓DAG)

·   ↓Gastrin, ↓histamine, ↓parietal cell activity

Class

Drug

Mechanism of action

DA₂ antagonist prokinetic

Metoclopramide

·   Peripheral DA₂ antagonist and 5HT₄ agonist -> ↑gastric motility, ↓pyloric sphincter tone

Macrolide prokinetic

Erythromycin

·   Motilin receptor agonist -> ↑gastric motility

(Pro-emetic)

Ipecac

·   Irritate gastric mucosa

·   Stimulate CTZ