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Part-1Review on Antiulcer Literaturewas the third H 2 receptor antagonist to be tested in humans and was similar to metiamidein its pharmacological profile, but did not cause agranulocytosis. Discovery of thismolecule reduced the necessity of surgical procedures for peptic acid diseases. Further,ranitidine 8 7 was introduced as more potent drug in 1981 with a much superior safetyprofile. 2 Third and most potent antagonist was famotidine 31 8 available for clinical use,being 20-50 times more potent than cimetidine and 6-10 times more potent thanranitidine. 32 nizatidine 33 9 and roxatidine 34 10 followed famotidine. Each of these drugsare rapidly absorbed and eliminated after oral administration. 35 H 2 receptor antagonistsare histamine congeners that contain a bulky cysteamine side chain in place of ethylaminemoiety of histamine. Earlier representatives of these groups such as burimamide andcimetidine retained the imidazole ring of histamine. This ring was further replaced byfuran as in ranitidine, by thiazole as in famotidine and nizatidine and piperazine andbenzene as in roxatidine. 1This helped to avoid unwanted cytochrome P450interactions. 36 HN NNH 2HNSNHistamine 3Burimamide 4NHNHHNNSMetiamide 5NHSNHHNNSCimetidine 6NHNNHCNN S NHNO 2NHORanitidine 7NH 2SNH 2H 2 NNNSFamotidine 8NSO 2 NH 210