Clinical and pharmacological characteristics of antiulcer drugs

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Antiulcer Drugs: Clinical and Pharmacological Characteristics

Antiulcer drugs act by one or more of three mechanisms: reducing gastric acid secretion, neutralizing existing acid, or enhancing mucosal defense. They are used principally for peptic ulcer disease (PUD), NSAID-associated ulcers, stress ulcers, GERD, and Zollinger-Ellison syndrome.

1. Proton Pump Inhibitors (PPIs)

Drugs: Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole

Mechanism

PPIs are prodrugs (benzimidazole derivatives) activated in the acidic environment of the secretory canaliculus of parietal cells. The activated sulfenamide covalently and irreversibly binds the H⁺/K⁺-ATPase ("proton pump"), blocking the final common pathway of all acid secretion. Because new pump synthesis is needed to restore acid output, the duration of action exceeds the short plasma half-life (~1–2 hours). A single daily dose suppresses ~70% of 24-hour acid output; twice-daily dosing suppresses ~95%.

Clinical Use

First-line for peptic ulcer healing, eradication-based regimens for H. pylori, NSAID-associated ulcers, GERD, and Zollinger-Ellison syndrome
Dose equivalent of omeprazole 20 mg once daily heals >85% of NSAID-induced duodenal ulcers and ~85% of gastric ulcers within 8 weeks
Double-dose PPI (omeprazole 40 mg twice daily) increases H. pylori eradication rates by ~10% and is preferred in combination regimens
For stress ulcer prophylaxis in ICU patients, PPIs and H₂-blockers are approximately equally effective; some data favor PPIs

Standard Doses (Goldman-Cecil Medicine, Table 124-1)

Drug	Peptic Ulcer	GERD Maintenance	ZES
Omeprazole	20–40 mg/day	20 mg/day	Up to 120 mg/day
Lansoprazole	15–30 mg/day	15 mg/day	High-dose
Pantoprazole	40 mg/day	40 mg/day	IV available
Esomeprazole	40 mg/day	20 mg/day	—

Adverse Effects

Generally well tolerated; may raise serum gastrin (can mimic Zollinger-Ellison on gastrin assay)
Long-term use: risk of C. difficile, pneumonia (debated), hypomagnesemia, vitamin B₁₂ deficiency, fractures (high-dose, prolonged use)
Drug interactions via CYP2C19 (omeprazole > pantoprazole/rabeprazole)

2. H₂-Receptor Antagonists (H₂RAs)

Drugs: Cimetidine, ranitidine (withdrawn in many countries), famotidine, nizatidine

Mechanism

Competitive, reversible antagonists at histamine H₂ receptors on the basolateral membrane of parietal cells. Block histamine-stimulated acid secretion but have less effect on meal-stimulated or acetylcholine-stimulated acid output. Reduce basal and nocturnal acid output effectively; less complete suppression than PPIs.

Clinical Use

Heal ~70% of NSAID-induced ulcers within 8 weeks at standard doses (equivalent to ranitidine 300 mg twice daily)
Higher doses (famotidine 40 mg twice daily) required for prevention of NSAID-associated gastric ulcers
Standard doses partially prevent NSAID-induced duodenal ulcers but are insufficient for gastric ulcers
Useful for stress ulcer prophylaxis in ICU; first-line in some pregnancy contexts (famotidine preferred)
Largely superseded by PPIs for most indications but still used for mild/intermittent symptoms

Adverse Effects

Cimetidine (most interactions): inhibits CYP1A2, CYP2C9, CYP2D6, CYP3A4; antiandrogenic effects (gynecomastia, impotence); mental status changes in elderly
Famotidine/nizatidine: minimal drug interactions; generally safe
Tachyphylaxis with continuous use (tolerance develops within days); less pronounced with intermittent dosing

3. Potassium-Competitive Acid Blockers (P-CABs)

Drug: Vonoprazan (approved in Japan, US, and increasingly elsewhere)

Mechanism

Reversibly and potassium-competitively inhibits H⁺/K⁺-ATPase. Unlike PPIs, does not require acid activation, works rapidly, and provides more stable and durable acid suppression (longer half-life at the pump). Less subject to CYP2C19 polymorphism.

Clinical Use

Vonoprazan 20 mg twice daily is incorporated into modern H. pylori triple-therapy regimens as an alternative to a PPI
Achieves comparable or superior H. pylori eradication rates vs. standard PPI-based regimens
Used for PUD healing and GERD

4. Antacids

Examples: Magnesium hydroxide, aluminum hydroxide, calcium carbonate, sodium bicarbonate, combination formulations (Maalox, Mylanta)

Mechanism

Directly neutralize hydrochloric acid in the gastric lumen, raising intragastric pH. No effect on acid secretion. Rapid onset, short duration of action.

Clinical Use

Symptomatic relief of heartburn and dyspepsia
Adjunctive in ulcer healing (historical role; largely replaced by acid secretion inhibitors)
High-dose antacid therapy (e.g., 120 mEq/dose 7 times daily) is as effective as H₂RAs for ulcer healing but impractical

Adverse Effects

Magnesium-containing: diarrhea, hypermagnesemia in renal failure
Aluminum-containing: constipation, phosphate depletion (osteomalacia with chronic use), aluminum toxicity in renal failure
Calcium carbonate: acid rebound, hypercalcemia, milk-alkali syndrome
Sodium bicarbonate: systemic alkalosis, sodium overload
All antacids can interfere with absorption of other drugs (fluoroquinolones, tetracyclines, iron, levothyroxine) — separate by ≥2 hours

5. Cytoprotective/Mucosal Protective Agents

5a. Sucralfate

Mechanism: In an acidic environment, sucralfate (aluminum sucrose sulfate) polymerizes into a viscous, paste-like material that adheres to ulcer craters, forming a physical barrier against acid, pepsin, and bile. Also stimulates prostaglandin E₂ synthesis and mucus secretion.

Clinical Use:

Heals duodenal ulcers comparably to H₂RAs (90% at 4 weeks)
Effective for stress ulcer prophylaxis (equivalent to H₂RAs, lower risk of ventilator-associated pneumonia in some studies)
Must be taken on empty stomach (4 times daily); drug absorption may be impaired

Adverse Effects: Constipation (aluminum content); aluminum toxicity in renal failure; impairs absorption of quinolones, digoxin, phenytoin, tetracyclines

5b. Misoprostol (Prostaglandin E₁ Analogue)

Mechanism: Synthetic PGE₁ analogue. Binds mucosal EP₃ receptors → inhibits adenylyl cyclase → reduces cAMP → decreases acid secretion. Also enhances mucosal defense: stimulates mucus and bicarbonate secretion, increases mucosal blood flow.

Clinical Use:

Prevention of NSAID-associated gastric and duodenal ulcers (200 μg four times daily); misoprostol and PPIs are equally effective for NSAID ulcer prophylaxis
Heals NSAID-induced ulcers comparably to H₂RAs
Adherence is the limiting factor — GI side effects reduce compliance; <80% adherence is associated with >2-fold increased ulcer risk vs. full adherence
Also used as an abortifacient/cervical ripening agent (obstetric use)

Adverse Effects: Dose-dependent diarrhea and abdominal cramping (most common, limits use); contraindicated in pregnancy (uterotonic)

5c. Bismuth Compounds

Examples: Bismuth subsalicylate (Pepto-Bismol), colloidal bismuth subcitrate (De-Nol)

Mechanism: Coat the ulcer base, stimulate mucus and bicarbonate secretion, and have direct bactericidal activity against H. pylori (disrupt cell wall and metabolism).

Clinical Use:

Core component of bismuth-based quadruple therapy for H. pylori (PPI + bismuth + tetracycline + metronidazole × 14 days → ~85–90% eradication)
Particularly useful in areas of high clarithromycin resistance

Adverse Effects: Black stools and tongue (harmless; must warn patients); encephalopathy with excessive or prolonged use; contains salicylate (avoid in aspirin-hypersensitive patients, Reye syndrome risk in children)

6. H. pylori Eradication Regimens

Because H. pylori causes 50–90% ulcer recurrence if untreated, antibiotic eradication is mandatory after ulcer confirmation. Regimens evolve based on local resistance patterns.

Regimen	Components	Duration	Eradication Rate
Standard triple therapy	PPI (double-dose) + amoxicillin + clarithromycin	14 days	~80% (low-resistance areas)
Bismuth quadruple	PPI + bismuth + tetracycline + metronidazole	14 days	85–90%
Concomitant (non-bismuth) quadruple	PPI + amoxicillin + clarithromycin + metronidazole (all together)	14 days	85–90%
Sequential	PPI + amoxicillin × 5 days, then PPI + clarithromycin + metronidazole × 5 days	10 days	~80%
P-CAB-based triple	Vonoprazan + amoxicillin + clarithromycin	14 days	≥90%

Clarithromycin resistance now ranges 10–50% in many regions; bismuth quadruple or susceptibility-guided therapy is increasingly preferred as first-line.

Summary Comparison

Drug Class	Onset	Acid Suppression	Mucosal Protection	Main Use
PPIs	1–4 days (full effect)	+++++	No	PUD, GERD, H. pylori, ZES
P-CABs (vonoprazan)	Rapid (hours)	+++++	No	PUD, H. pylori
H₂RAs	Hours	+++	No	Mild PUD, prophylaxis
Antacids	Minutes	+	No	Symptomatic relief
Sucralfate	Hours	No	+++	Stress ulcer, PUD
Misoprostol	Hours	++	+++	NSAID ulcer prevention
Bismuth	Hours	No	++	H. pylori eradication

Sources:

Goldman-Cecil Medicine, International Edition — pp. 1448–1451 (Peptic Ulcer Disease treatment, Tables 124-1, 125-4)
Sleisenger and Fordtran's Gastrointestinal and Liver Disease — pp. (block 4, Peptic Ulcer bleeding)

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