Atropine gastric ulcers

Antagonists. Most of the so-called Hi-antihistamines also block other receptors, including M-cholinoceptors and D-receptors. Hi-antihistamines are used for the symptomatic relief of allergies (e.g., bamipine, chlorpheniramine, clemastine, dimethindene, mebhydroline pheniramine) as antiemetics (meclizine, dimenhydrinate, p. 330), as over-the-counter hypnotics (e.g., diphenhydramine, p. 222). Promethazine represents the transition to the neuroleptic phenothiazines (p. 236). Unwanted effects of most Hi-antihistamines are lassitude (impaired driving skills) and atropine-like reactions (e.g., dry mouth, constipation). At the usual therapeutic doses, astemizole, cetrizine, fexofenadine, and loratidine are practically devoid of sedative and anticholinergic effects. Hj-antihistamines (cimetidine, ranitidine, famotidine, nizatidine) inhibit gastric acid secretion, and thus are useful in the treatment of peptic ulcers. 

Selective muscarinic receptor blocker. It inhibits gastric secretion. Thus is effective in peptic ulcer patients and promotes ulcer healing. It does not produce atropinic side effect (due to blockade of and M3 receptors). 

During the extraction procedure a partial racemisation takes place. The racemate of L-hyoscyamine is atropine. The pharmacologically active isomer is L-hyoscyamine, which has double the activity of the racemic atropine. L-hyoscyamine is used for the inhibition of gastric secretion in cases of gastric and duodenal ulcer. 

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