Agent nonsedating antihistamine
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Antihistamines are inhibitors of histamine receptors. H1-antihistamines, inhibit competitively H1 receptors and the corresponding effects i. They do not inhibit antigen/antibodies reactions, nor histamine release, they inhibit H1 effects.
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.
It is usual to classify H1-antihistamines into two classes: old ones, called first-generation agents, which are sedating and recent ones, called second-generation agents which have slight or no sedating effects because they do not cross the blood-brain barrier.This adverse effect is linked to their effect on potassium channels leading to slowing of repolarization rate.H1-antihistamines without sedating effect currently marketed are mequitazine, cetirizine, loratadine, mizolastine, fexofenadine because they do not cross blood-brain and thus their effects remain peripheral.New H1-antihistamines induce only exceptionally drowsiness. This possibility, even rare, must however be taken into account, particularly at time of a first prescription.It is not advised to prescribe a sedating a H1-antihistamine to infants because, although this is not documented, it could increase the risk of sudden death.