Pharma & Specialty Chemical Standards

Cetirizine, 4-(4-chlorophenyl)-1-piperazineethanol (C21H25ClN2O2, molecular weight 372.45 g/mol), is a second-generation piperazine-derived antihistamine. Its structure features a piperazine ring conjugated to a chlorophenyl group and ethanol moiety. Therapeutically, it treats allergic rhinitis and urticaria. Physicochemically, it is a white crystalline solid with low water solubility (logP ~2.5), pKa ~8.5, and high lipophilicity. Mechanistically, it selectively antagonizes peripheral H1 receptors, inhibiting histamine-mediated vasodilation and pruritus, while minimal CNS penetration reduces sedation. Its stability and oral bioavailability enhance clinical utility.