Cetirizine-d8 (hydrochloride) is intended for use as an internal standard for the quantification of cetirizine , (R)-cetirizine , and (S)-cetirizine by GC- or LC-MS. Cetirizine is a bioactive carboxylated metabolite of hydroxyzine that acts as a selective histamine H1 receptor antagonist (Ki = 10 nM). As a second generation antihistamine, it is non-sedating due to low lipophilicity, which prevents blood-brain barrier transit. Cetirizine is a racemic mixture composed of equal amounts of two enantiomers, (R)-cetirizine and (S)-cetirizine, with pharmacological activity residing primarily in the (R) isomer. Cetirizine inhibits eosinophil chemotaxis and leukotriene B4 (LTB4; ) release independent from H1 antagonism. It inhibits aerosol histamine-induced bronchospasm in guinea pigs (ED50 = 100 μg/kg, p.o.). Formulations containing cetirizine have been used in the treatment of allergic rhinitis and chronic urticaria.
