Subject:

Preparatory Mindset

GI drugs target specific components of digestion. Antacids neutralize acid, H2 blockers and PPIs suppress acid production (PPIs are the most potent). Prokinetics (metoclopramide) increase motility. Anti-emetics work via different pathways (H1, M1, D2, 5-HT3). Know which receptor each antiemetic blocks.

Core Concepts

Ch04: Gastrointestinal

Key Drug Table — Anti-Peptic Ulcer Drugs

| Drug Class | Drug | MOA | Key Points |
|-----------|------|-----|-----------|
| PPI (Proton Pump Inhibitor) | Omeprazole | Irreversibly inhibits H+/K+-ATPase (parietal cell) | Most potent acid suppressant; for GERD, PUD, Zollinger-Ellison |
| H2 Antagonist | Cimetidine, Famotidine, Ranitidine | Blocks H2 receptors on parietal cells → ↓ acid | Cimetidine: CYP450 interactions (↑ warfarin/theophylline) |
| M1 Antagonist | Pirenzepine | Blocks M1 receptors (selective) | ↓ Gastric acid, fewer systemic side effects |
| Gastrin Receptor Blocker | Proglumide | Blocks gastrin receptors | ↓ Acid secretion induced by gastrin |
| Prostaglandin Analogue | Misoprostol | ↑ Mucus + HCO3- secretion; ↓ acid | Prevent NSAID-induced ulcers; contraindicated in pregnancy (abortifacient) |
| Antacids | Al(OH)3, Mg(OH)2 | Neutralize gastric acid | Rapid symptom relief; drug interactions (chelation) |
| Mucosal Protectant | Sucralfate | Forms protective barrier over ulcer | Requires acidic pH for activation |
| Bismuth Compound | Potassium Bismuth Citrate | Forms protective coating | Used for H. pylori eradication |

Key Relationships: Regulation of Gastric Acid


Vagus (ACh) ——> M1 receptor  ——↘
Gastrin ———-> Gastrin receptor —→ H+/K+-ATPase → H+ secretion
Histamine (ECL) -> H2 receptor ———↗

Drugs acting on ECL cells: Cimetidine (H2 antagonist) blocks histamine released from ECL cells → ↓ acid secretion indirectly.

Exam-Frequency Core Points (from exam notes)

III. Drugs Acting on the Digestive System (core: acid‑suppressing agents, exam frequency: ~35%)

| Representative Drug | Core Exam Points | Frequency | 【Must-Know Details】 |
| --- | --- | --- | --- |
| Omeprazole (Proton Pump Inhibitor / PPI) | Mechanism: specifically inhibits the H⁺‑K⁺‑ATPase (proton pump) on gastric parietal cells, blocking gastric acid secretion at the final step; potent and long‑lasting acid suppression; also has anti‑Helicobacter pylori activity | ★★★ | ❶ Currently the most potent acid‑suppressing drug class; first‑choice treatment for gastric and duodenal ulcers, gastroesophageal reflux disease, and Zollinger‑Ellison syndrome; core component of the quadruple regimen for H. pylori eradication; ❷ Long‑term use requires vigilance for adverse effects such as osteoporosis and vitamin B₁₂ deficiency |

真题题目区

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[ 【Drugs Acting on the Digestive System】](https://app.notion.com/p/Drugs-Acting-on-the-Digestive-System-38af1f80e97c800b8589ed4ec24e4042?pvs=21)

High-Yield Points

PPIs (omeprazole): most potent acid suppression — irreversible H+/K+ ATPase inhibition

H2 blockers (ranitidine): competitive histamine blockade at parietal cells

Antacids: rapid symptom relief but short duration

Metoclopramide: prokinetic — D2 antagonist, 5-HT4 agonist

Ondansetron: 5-HT3 antagonist — for chemotherapy-induced nausea

Sucralfate: forms protective barrier over ulcer — requires acidic pH to activate

Topic Summary

Peptic ulcer treatment: PPIs are most effective acid suppressors. H2 blockers are alternatives. Anti-emetics target specific receptors: motion sickness = antihistamines/anticholinergics, chemotherapy = 5-HT3 antagonists, delayed = NK1 antagonists.

Pharmacology Notes