H2 Antihistamines (famotidine)
H2 receptor antagonist — blocks histamine-mediated gastric acid secretion
- Response rate
- Effective for GI symptoms
- Onset
- Hours–days
- Route
- Oral twice daily
- Line
- 1st
- IgM effect
- N/A
Evidence summary
First-line for GI symptoms (abdominal pain, diarrhea, nausea). Inhibit gastric acid secretion via H2 receptors. Combined with H1 antihistamines, they also reduce overall mast cell mediator release. Often supplemented or replaced by proton pump inhibitors for severe GI disease.