Ranitidine is a histamine H-2 receptor antagonist similar to cimetidine and famotidine. Competitively inhibits the binding of histamine to receptors on gastric parietal cells (designated as the H-2 receptor), thus reducing basal and nocturnal gastric acid secretion. It also decreases the amount of gastric acid released in response to stimuli such as food, caffeine, insulin etc. Ranitidine is 5-12 times as potent as cimetidine as a histamine receptor antagonist while having less affinity than cimetidine for the cytochrome hepatic enzyme system. As a result, ranitidine is much less likely than cimetidine to interact with other drugs, although drug interactions with ranitidine do exist. Similar to other H2-receptor antagonists, the main use of ranitidine is in the treatment of gastrointestinal disorders. In June 1983 ranitidine was approved by the FDA for use in managemnt of duodenal ulcer and hypersecretory states. Ranitidine is administered orally and by intravevous injection or infusion.