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 Cetirizine Brand name:- Alerid,cetzine,zirtin,sizon 10mg tab 5mg/5ml syr.  Cetirizine is an antihistaminic medication. It treats allergy symptoms such as itching, swelling, and rashes by blocking the effects of a chemical messenger (histamine) in the body. Mechanism of action:- Cetirizine is a fast-acting, highly selective antagonist of the peripheral histamine H1 receptor. The H1-receptors inhibited by cetirizine are primarily on respiratory smooth muscle cells, vascular endothelial cells, immune cells, and the gastrointestinal tract. Unlike first-generation antihistamines such as diphenhydramine and doxylamine, cetirizine does not cross the blood-brain barrier to a large extent, avoiding the neurons of the central nervous system. As a result, cetirizine produces minimal sedation compared to many first-generation antihistamines. Given its antagonism with histamine H1-receptors, cetirizine effectively reverses many of the effects of histamine. Like other second-generation ant...