A patient with H. pylori-associated peptic ulcer disease is prescribed a bismuth quadruple regimen (bismuth, PPI, metronidazole, tetracycline). What is the primary mechanism by which bismuth subsalicylate/tripotassium dicitratobismuthate exerts anti-H. pylori activity?

• A Inhibition of H. pylori urease, preventing ammonia production and pH buffering
• B Chelation of iron in gastric mucosa preventing H. pylori growth
• C Precipitation on H. pylori cell surface and outer membrane disruption; also inhibits bacterial adhesion to gastric epithelium and impairs virulence factor secretion ✓
• D Generation of reactive oxygen species via Fenton chemistry toxic to H. pylori

Explanation

Bismuth salts exert multiple anti-H. pylori mechanisms. Bismuth ions precipitate on the bacterial cell surface, disrupting the outer membrane and inhibiting membrane protein function. They inhibit H. pylori adhesion to gastric epithelial cells (blocking binding to Lewis antigen groups), suppress H. pylori virulence factors (urease and phospholipases), and also bind to the H. pylori cell wall peptidoglycan. Bismuth accumulates in H. pylori vacuoles and can directly kill the organism. Bismuth quadruple therapy is the preferred salvage regimen after failure of standard triple therapy and increasingly used as first-line where clarithromycin resistance is high (>15%). Urease inhibition occurs but is not the primary mechanism.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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