Non sedating h1 antihistamines

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Certain H1 antagonists, such as promethazine, have a local anesthetic effect.Other H1-antihistamines having an important antimuscarinic activity like diphenhydramine and dimenhydrinate, are used in preventive and curative treatment of motion sickness, but scopolamine which has no antihistamine effect seems more effective than them in preventive treatment.

H1-antihistamines have been used for more than fifty years in treating various allergic manifestations. H1-antihistamines which penetrate into brain elicit, by inhibiting stimulant effect of histamine, drowsiness.In case of overdose, loratadine can cause sedation and antimuscarinic effects.Cetirizine, carboxyl derivative of hydroxyzine which is used as a sedative and anxiolytic, in addition to its H1-antihistamine effect, inhibits release of various cytokines and leukotrienes.The two first H1-antihistamines without sedating effect to be marketed were terfenadine and astemizole.They were withdrawn from the market because they could induce ventricular arrhrythmias, prolongation of QT interval which can lead to torsades de pointes.

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