Histamine receptor antagonists tolerance

The longstanding use in some countries of hydroxyzine, a centrally-acting Hi-histamine receptor antagonist, is supported by positive findings in controlled trials in GAD (Ferreri and Hantouche 1998 Lader and Scotto 1998). Hydroxyzine promotes sleep and its anxiolytic effects have an early onset. Although it causes sedation, tolerance to this effect often occurs and effects on psychomotor performance are smaller than with benzodiazepines (de Brabander and Deberdt 1990). It is well-tolerated and withdrawal effects have not been reported. Although the evidence for its efficacy is not large, hydroxyzine provides an option for some patients with GAD for whom standard treatments are unsuitable. 

Cimetidine (Tagamet) H2 Histamine Receptor Antagonist. Duodenal/gastric ulcer, hypersecretion of acid, GERD. Well tolerated. Diarrhea, dizziness, rash, headache, confusion, somnolence, decreased libido, impotence, gynecomastia. Rarely, blood dyscrasias, hepatotoxicity and renal toxicity. 

A 25-year-old man with symptoms of acute gastroenteritis took Pepto-Bismol, a total of eight caplets over 6 hours. About 30 minutes after the last dose, he developed generalized acute urticaria. He had previously tolerated Pepto-Bismol well, but had presumably become sensitized. He was successfully treated with intravenous fluids and histamine Hi receptor antagonists. 

Nathan PJ, Boardley R, Scott N, Berges A, Maruff P, Sivananthan T et al (2013) The safety, tolerability, pharmacokinetics and cognitive effects of GSK239512, a selective histamine H3 receptor antagonist in patients with mild to moderate Alzheimer s disease A preliminary investigation. Curr Alzheimer Res 10 240-251... 

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