Levocetirizine dihydrochloride is a highly potent, non-sedating second- generation antihistamine. It functions by acting as a highly selective, high-affinity inverse agonist at the peripheral histamine H1 receptors, completely blocking the cellular actions of endogenous histamine molecules released by mast cells during allergic responses. Because it is the pure R-enantiomer, it possesses a much higher binding affinity and slower dissociation rate from the target receptors compared to the racemic mixture, effectively preventing vascular permeability, itching, mucosal swelling, and systemic rhinorrhea (runny nose) with a low incidence of central somnolence.