GIT Pharm – Gastric fluid

Master answer

• Options for preventing ulceration:
  • 1) Prevent acid secretion
  • 2) Eliminate acid already present
  • 3) Protect mucosa from acid

• H₂-receptor antagonists:
  • Competitively (and selectively) antagonise H₂ receptors on parietal cells
  • Dampened parietal cell response to ACh and gastrin when histamine blocked
• Proton pump inhibitors:
  • Prodrug
  • Intestinal absorption into parietal canaliculi
    • Converted to active form
  • Binds covalently to H+/K+ ATPase
• Sucralfate
  • Sucrose sulphate^– / aluminium⁺ salt, which dissociates
  • Sucrose sulphate binds to positively charged proteins on damaged mucosa
    • Forms a barrier, protecting them from acid
  • Stimulates mucosal prostaglandin and bicarbonate secretion
• Antacids
  • Weak bases, reacting with HCl to form a salt and water
  • Sodium bicarbonate:
    • NaHCO₃ + HCl -> NaCl + H₂O + CO₂
    • Belching, and NaCl may be an issue in CKD / CCF
  • Calcium carbonate:
    • CaCO₃ + 2HCl -> CaCl₂ + H₂O + CO₂
    • Belching, calcium toxicity, metabolic acidosis
  • Magnesium and aluminium hydroxide:
    • No belching (no CO₂₊)
    • No absorption of the metal
    • Magnesium salts cause diarrhoea, aluminium salts cause constipation

Mooney 2016

Answer by Mooney