What is the mechanism of action for histamine receptor antagonists as antacids?

Histamine receptor antagonists, commonly known as H2 blockers, function primarily by blocking H2 receptors in the stomach. This mechanism inhibits the action of histamine, a key stimulant of gastric acid secretion. When histamine binds to H2 receptors on parietal cells in the gastric mucosa, it triggers the production and release of gastric acid. By antagonizing these receptors, H2 blockers reduce the formation of gastric acid, leading to decreased acidity in the stomach and relief from conditions related to excess acid, such as gastroesophageal reflux disease (GERD) or peptic ulcers.

This distinct approach sets H2 blockers apart from other medications classified as antacids. While neutralization of stomach acid involves the direct buffering of existing acid through compounds like magnesium or aluminum hydroxide, and binding to proton pumps is the mechanism utilized by proton pump inhibitors (PPIs) which inhibit acid secretion by blocking the proton pumps themselves, histamine receptor antagonists specifically target the histamine receptors to limit acid production. Thus, blocking H2 receptors in the gut is the method by which histamine receptor antagonists exert their therapeutic effects.