Constipation famotidine

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. 

The interactions with cimetidine are well established, well documented and of clinical importance. The incidence is uncertain hut most patients could be affected. Those taking amitriptyline, desipramine, doxepin, imi-pramine or nortriptyline who are given cimetidine should be warned that adverse effects such as mouth dryness, urine retention, blurred vision, constipation, tachycardia, postural hypotension may be more likely to occur. Other tricyclic antidepressants would be expected to be similarly affected. If symptoms are troublesome reduce the dosage of the antidepressant (33 to 50% has been suggested) or replace the cimetidine with ranitidine, which does not appear to interact. Other H2-ieceptor antagonists that do not cause enzyme inhibition (e.g. famotidine and nizatidine) would also not be expected to interact. 

General side effects The most frequent side effects reported by patients receiving 40 mg of famotidine in clinical trials, with an incidence of over 1% were headache (4.7%), diarrhoea (1.7%), dizziness (1.3%) and constipation (1.2%). However, the incidence of these reported side effects was similar between famotidine and placebo (http //www.acc essdata.fda.gov/drugsatfda docs/anda/2001/75311 Famotidine Pmtlbl.pdf ). 

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