Setin Mechanism of Action

Pharmacology: Pharmacodynamics: Cetirizine hydrochloride is a piperazine derivative secondary generation and long-acting non-sedative antihistamine. Cetirizine is the carboxylic acid metabolite of hydroxyzine. Cetirizine is a potent and selective antagonist of peripheral H₁ receptor. The increased polarity of Cetirizine may decrease distribution of the drug into the CNS, resulting in reduced potential for adverse CNS effect compared with some first generation antihistamine.
Pharmacokinetics: Absorption: Cetirizine is rapidly absorbed from the gastrointestinal tract after oral doses and peak plasma concentrations occur within about an hour. Food delays the time to peak plasma concentration but does not decrease the amount of drug absorbed.
Distribution: Cetirizine appears to be extensively distributed into many body tissues, fluids, and milk in humans. Cetirizine is approximately 93% bound to plasma proteins.
Metabolism: Cetirizine undergoes a low degree of first pass metabolism in the liver.
Elimination: About two-thirds of the dose of Cetirizine is excreted unchanged in urine. The terminal half-life is approximately 10 hours.