Anatomical Therapeutic Chemical Classification System
Cimetidine is a histamine H2-receptor antagonist which rapidly inhibits both basal and stimulated gastric secretion of acid and reduces pepsin output. It is a reversible, competitive antagonist, and is used as an anti-ulcer drug.
Famotidine is a potent competitive H2-receptor antagonist. Famotidine has a rapid onset of action and, at the recommended doses, has a long duration of action and is highly effective at relatively low blood concentrations.
Ranitidine is a specific rapidly acting histamine H2-antagonist. It inhibits basal and stimulated secretion of gastric acid, reducing both the volume and the acid and pepsin content of the secretion. Ranitidine has a relatively long duration of action and so a single 150 mg dose effectively suppresses gastric acid secretion for twelve hours.