H2 antihistamines

The discovery of the antiulcer activity of H2 antihistamine antagonists has revolutionized the treatment of that disease. A benzimidazole. Omeprazole (55), inhibits gastric secretion and subsequent ulcer formation by a quite different mechanism. Studies at the molecular level suggest that this compound inhibits K /H dependent ATPase and consequently shuts down the proton pumping action of this enzyme system. 

Therapeutic advantages resulting from new chemical entities with improved receptor selectivity were mentioned earlier in this chapter and are described in detail in later chapters. Such drugs include a- and B-selective adrenoceptor agonists and antagonists, Hi and H2 antihistamines, nicotinic and muscarinic blocking agents, and receptor-selective steroid hormones. All... 

The H2 antihistamines are used in the treatment of duodenal ulcers, gastric ulcers, gastroesophageal reflux disease (GERD), pathological hypersensitivity disorders, and upper gastrointestinal bleeding in critically III patients and are sold OTC for acid indigestion (45). 

They also are included in multidrug treatment protocols for eradication of H. pylori in treatment of peptic ulcers and before surgery to prevent aspiration pneumonitis. Like Hi antihistamines, H2 antihistamines are inverse agonists that block the basal level of activity at this receptor. Combinations of Hi and H2 antihistamines are useful in idiopathic urticaria not responding to Hi antihistamines alone and in itching and flushing of anaphylaxis, pruritis, and contact dermatitis. 

Bismuth-containing preparations (e.g., those containing colloidal bismuth subcitrate) have effects similar to those of sucralfate, apparently because of their similar physical properties and coating effects. A combination of ranitidine-bismuth citrate is used with clarithromycin for eradication of H. pylori in the treatment and prevention of recurrence of duodenal ulcers. Combinations of bismuth subcitrate with other antibiotics and with H2 antihistamines also are used. Bismuth subsalicylate is used in this way as well. 

Cost inexpensive over-the-counter formulations are available for both HI antihistamines and H2 antihistamines. Second-generation HI antihistamines are generally more expensive than first-generation and may not be covered by insurance carriers due to the availability of over-the-counter formulations. 

Tung, R., Kagey-Sobotka, A., Plant, M., and Lichtenstein, L. M., 1982, H2 antihistamines augment antigen-induced histamine release from human basophils in vitro, J. Immunol. 129 2113-2115. 

HI antagonists or HI blockers and possibly H2 antihistaminics should be combined with the above-mentioned steroids, and should be given 30 min before ICM injection. 

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