Pharma & Specialty Chemical Standards

Diphenhydramine, IUPAC name 2-(acetyloxy)-N,N-dimethyl-4-(2-hydroxyethyl)aniline, is a first-generation antihistamine with molecular formula C17H21NO and molecular weight 255.35 g/mol. Structurally, it belongs to the ethylenediamine class, featuring a diphenylmethane core with an acetyl group and a dimethylaminoethyl chain. Its lipophilicity (logP ~1.4) and weak basicity (pKa ~9.5) enhance membrane permeability and receptor binding. Therapeutically, it alleviates allergic reactions, insomnia, and motion sickness. Mechanistically, it acts as a competitive H1 histamine receptor antagonist, inhibiting histamine-mediated vasodilation, bronchoconstriction, and pruritus. Its sedative effects stem from central nervous system penetration due to low molecular weight and lipophilicity.