Chemical and biologic differences between various H2-receptor antagonists.

After a brief historical review, the common chemical features of various H2-receptor antagonists are discussed, demonstrating that an imidazole, furan, thiazole, and the piperidinylmethylphenoxy moiety can serve as an aromatic nucleus of histamine H2-receptor antagonists. Furthermore, it is paradigmatically illustrated that the histamine H2-receptor antagonists in use or under clinical investigations inhibit, in a competitive and surmountable manner, parietal cell acid secretion and histamine H2-receptor-linked adenylate cyclase. Furthermore, toxicologic problems of unsurmountable and/or or long-acting histamine H2-receptor antagonists (tiotidine, loxtidine, and SK&F 93479) are discussed.