60 years. Fexofenadine is an active metabolite of the second generation histamine H1 receptor antagonist (antihistamine). Fexofenadine hydrochloride, the active ingredient of ALLEGRA tablets, is a histamine H1-receptor antagonist with the chemical name (±)-4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-butyl]-α,α-dimethylbenzene acetic acid hydrochloride (Fig. 1). Fexofenadine is used to