H2 Blockers

Introduction

• Other agents: cimetidine, famotidine, and nizatidine 
• Mechanism 
  • indirectly inhibit proton pump by blocking stimulation via H₂ receptors on parietal cells and ECL cells
    • leads to ↓ H⁺ secretion by parietal cells
  • no effect on gastic emptying time
• Clinical use
  • peptic ulcer
  • gastritis
  • GERD
  • Zollinger-Ellison syndrome
• Toxicity
  • cimetidine
    • potent inhibitor of P-450 
    • antiandrogenic effects 
      • results in gynecomastia, impotence, and ↓ libido in males
    • crosses blood-brain barrier
      • results in confusion, dizziness, and headaches
      • avoid in the elderly and mentally unstable
    • crosses placenta
  • cimetidine and rantidine ↓ creatinine clearance
  • other H₂ blockers have fewer side effects