Add time:08/27/2019         Source:sciencedirect.com

Publisher SummaryThis chapter describes fexofenadine hydrochloride (FEX), its nomenclature, formulae, methods of preparation, physical properties, and methods of analysis, stability, drug metabolism, and pharmacokinetics. FEX is obtained as a white to off-white crystalline powder. FEX is a nonsedating, second-generation H1 antihistamine, which acts as a reversible and competitive inhibitor at H1 histamine receptor sites. The drug is an active carboxylic acid metabolite of terfenadine, and provides all the therapeutic benefits of terfenadine, while avoiding the serious cardiotoxic and drug interaction risks of the parent drug, and is therefore, considered as a relatively safe alternative to terfenadine. The synthetic approach for preparation of FEX involves the reduction of a carboxylate derivative, 4-[4-[4-(hydroxybiphenylmethyl)-1-piperidinyl]-1-oxobutyl]-a,a-dimethyl benzene acetate; followed by hydrolysis with a base, for example alkali metal hydroxides, to get the carboxylic acid derivative FEX. FEX exists as a zwitterion in aqueous media at physiological pH. The drug has two ionization groups corresponding to free carboxylic group on the side chain and the substituted ring nitrogen, contributing to a pKa value of 4.25 and 9.53, respectively. FEX is stable under normal storage conditions, but the substance is stored in tight containers and protected from light and humidity. Photodegradation of FEX is studied using a stability indicating high performance liquid chromatography (HPLC) assay method.

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