Histamine receptor blocker

Drug therapy, if necessary, may be initiated with aluminum, calcium, or magnesium antacids sucralfate or cimetidine or ranitidine. Lansoprazole, omeprazole, and metoclopramide are also options if the patient does not respond to histamine-2 receptor blockers. 

The histamine-2 receptor blockers (H-2 blockers) are used to treat hyperacidity in the stomach, and the most commonly used medications are available over the counter (without prescription). The first one was cimetidine (brand name Tagamet), which is a very common cause of delirium, confusion, psychosis, and aggression in the elderly—especially at night. The other H-2 blockers, such as ranitidine (brand name Zantac) and famotidine (brand name Pepcid), can also cause these symptoms, which are quite rare with these two drugs. Cimetidine should be avoided in the elderly and those with a serious illness. The H-2 blockers can also cause depression, mania, and nightmares. Therapists will see many patients who are taking H-2 blockers, and the patients may not... 

Hj histamine receptor blockers can be grouped according to their chemical structures ethanolamine derivatives (diphenhydramine, clemastine) ethylenediamine derivatives (tripe-lennamine, pyrilamine) alkylamines (chloropheniramine, dexchlorpheniramine, brompheniramine) piperazines (cycUzine, meclizine, hydroxizine) phenothiazines (promethazine, trimeprazine) piperidines (cyproheptadine, diphenylpyraline) and others that do not belong to a specific chemical classification (terfenadine, astemizole). 

Oral 400 to 800 mg combined hydroxides per tablet, capsule, or 5 mL suspension H2 Histamine Receptor Blockers Cimetidine (generic, Tagamet, Tagamet HB )... 

Antihistamines are the most frequently used agents in the treatment of sneezing and watery rhinorrhea associated with allergic rhinitis. -Histamine receptor blockers, such as diphenhydramine, chlorpheniramine, loratadine, terfenadine and astemizole (see p. 422), are useful in treating the symptoms of allergic rhinitis caused by histamine release. Combinations of antihistamines with decongestants (see below) are effective when congestion is a feature of rhinitis. They differ in their ability to cause sedation, and their duration of action. 

H2-histamine receptor blockers alone or together. Hyperuricaemia, due to cell destruction, is prevented by allopurinol and iron and folate deficiency by replacement doses (due to the rapid response of the myeloproliferative erythron). Aspirin remains controversial. Low-dose aspirin (for antiplatelet action) may be used if the platelet coxmt remains high or thrombosis occurs despite the above treatment but is best avoided in patients with a history of haemorrhage. 

The use of premedication with steroids and Hi and Hg histamine receptor blockers can significantly reduce the adverse reactions to high osmolality contrast media. There are suggestions to extend their use to modify even the reactions to low osmolality contrast media. Pretesting of contrast media reactors by injecting 1 mL of the nonionic contrast medium has also been reported (539). 

V. cholerae is a gram-negative baciUus sharing similar characteristics with the family Enterobacteriaceae. Most pathology of cholera results from an enterotoxin (cholera toxin) produced by the bacteria. Conditions that reduce gastric acidity, such as the use of antacids, histamine-receptor blockers, or proton pump inhibitors or infections with Helicobacter pylori, increase the risk for clinical disease. Cholera toxin stimulates adenylate cyclase, which increases intracellular cAMP and results in inhibition of sodium and chloride absorption by microvillli and promotes the secretion of chloride and water by crypt cells. The toxin likely acts along the entire intestinal tract, but most fluid loss occurs in the duodenum. The net effect of the cholera toxin is isotonic fluid secretion (primarily in the small intestine) that exceeds the absorptive capacity of the intestinal tract (primarily the colon). This results in the production of watery diarrhea with electrolyte concentrations similar to that of plasma. 

Histaminei (Hj) receptors mediate such actions as bron-choconstriction and the contraction of smooth muscles in the gastrointestinal tract. Ebastine is a histamine,-receptor blocker. Terfenadine, astemizole, loratadine, and certirizine are second-generation antihistamine agents that are relatively nonsedating. Other H,-receptor antagonists currently undergoing clinical trials are azelastine, ebastine, and levo-cabastine (see also Figures 34 and 59). 

It is a peripherally selective piperidine histamine receptor blocker, which competitively antagonizes histamine at the Hj-receptor site. It is indicated in the temporary relief of symptoms caused by hay fever or other upper respiratory allergies (runny nose, sneezing, itchy/watery eyes, itching of the nose or throat) and in the treatment of chronic idiopathic urticaria. 

These observations were confirmed and extended by Hayden, Thomas and West with reports showing that Cu(II)2(aspirinate)4 and Cu(IIXsaUcylate)2 were more efifective in the aspirin-exacerbated Shay ulcer model than either the H,(Mepyramine) or H2(Metiamide) histamine receptor blockers, as shown in Table 6.19 [263]. It was also shown that Cu(II)(saUcylate)2 was more... 

Table 6.19. COMPARISON ON ORAL ANTIULCER ACTIVITY OF Cu(II)2(ASPIRI-NATE>4, Cu(1I)(SALICYLATE)2, and histamine receptor blockers IN THE ASPIRIN-PRETREATED SHAY RAT [263]...

Table 6.20. COMPARISON OF ORAL ANTIULCER ACTIVITY OF Cu(II)(SALICYLATE)2 AND HISTAMINE RECEPTOR BLOCKERS IN THE COLD-WATER STRESSED...

A. Relief of symptoms caused by excessive histamine effect (eg. ingestion of scombroid-contaminated fish or niacin and rapid intravenous administration of acetylcysteine). Diphenhydramine may be combined with cimetidine or another Hj histamine receptor blocker (see p 428). 

The present report describes the covalent conjugation of paclitaxel to y-carboxylic acids of poly-L-glutamic (PG) acid (CT-2103). Paclitaxel is a particularly appropriate molecule for conjugation to a polymer carrier because it is broadly active as an anti-tumour agent, yet it is difficult to deliver because it is highly hydrophobic. The commercial preparations of pacKtaxel use Cremophor and ethanol as solubilising agents. These have inherent toxicities and require slow infusions and premedications with corticosteroids and histamine receptor blockers. 

This second-generation histamine HI receptor blocker was put on the world market in the 1980s for the relief of symptoms associated with seasonal allergic rhinitis and chronic idiopathic urticaria [14], Janssen Pharmaceuticals marketed this dmg under the brand name Hismanal. The major benefit of these antihistamines was their... 

Hf and H Receptors. Histamine exerts its actions by binding to receptors on cell membranes. Two types of histamine receptors, the Hi and H2 receptors, are known specific agonists and antagonists exist for each of these receptors. Black et al. (55) differentiated H and H2 receptors with the compounds, 2-methylhistamine and 4 methylhistamine. 2-Methylhistamine is active on tissues with H receptors 4-methylhistamine is active on tissues with H2 receptors. Classical antihistaminic drugs were developed in the 1930 s these compounds block H but not H2 receptors. Among the clinically used H -blockers are derivatives of ethanolamine, ethylenediamine, alkylamine, piperazine and phenothiazine (32). These agents are valuable in the treatment of... 

This lack of complete effectiveness led to the hypothesis that a second type of histamine receptor existed. In 1972, Black et al. (55) discovered a new series of antagonists which they called H2 receptor blockers. Burimamide was the first highly effective H2 blocker, but it was poorly absorbed orally. The modified compound, metiamide, had better absorption but was found to cause granulocytopenia (57.58). Finally, cimetidine was tested and found to be a potent and relatively non-toxic antagonist (59). Cimetidine is now widely used clinically to treat duodenal ulcers, Zollinger-Ellison Syndrome and other gastric hypersecretory diseases (32). 

Belladonna alkaloids have an extremely broad pharmacological spectrum. In addition to their ability to block M-receptors, atropine and scopolamine also act on other receptors, thus showing corresponding effects. They can only block nicotinic cholinergic receptors, however, in significantly larger doses than those used in clinics. Atropine also exhibits properties of local anesthetics and histamine (Hj) receptor blockers. Atropine and... 

The effects of histamine on body tissues and organs can be diminished in four ways inhibition of histamine synthesis, inhibition of histamine release from storage granules, blockade of histamine receptors, and physiological antagonism of histamine s effects. Of these approaches, only the inhibition of histamine synthesis has not been employed clinically. The focus of this chapter is on Hi histamine receptor antagonists it provides a brief overview of the H2 blockers and the inhibitors of histamine release. More details can be found in Chapters 39 and 40. 

The development of H2-receptor antagonists was based on the observation that H4 antagonists had no effect on histamine-induced acid secretion in the stomach. Molecular manipulation of the histamine molecule resulted in drugs that blocked acid secretion and had no H4-agonist or antagonist effects. Like the other histamine receptors, the H2 receptor displays constitutive activity, and some H2 blockers are inverse agonists. 

The i.c.v. injection of apamin or charybdotoxin, specific blockers of the SK and BK type of Ca2+-activated K+ channels, respectively, prevented the antinociception mediated by tricyclic antidepressants and H1 histamine receptor antagonists whereas 0C2 adrenoceptor-mediated supraspinal analgesia did not depend on the activation of these K+ channels (Table 1). 

Histamine H2-receptor blockers -idine Cimetidine, ranitidine Gastric ulcers (27)... 

The term antihistamine, without a modifying adjective, refers to the classic Hi receptor blockers. These compounds do not influence the formation or release of histamine, but rather they competitively block the receptor-mediated response of a target tissue. [Note This contrasts with the action of cromolyn (see p. 220), which inhibits the release of histamine from mast cells and is useful in the treatment of asthma.] The H receptor blockers can be divided into first- and second generation drugs.(Figure 40.5). The first generation drugs are still widely used because they are effective and inexpensive. 

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