Cetirizine Hydrochloride, known by trade names Zyrtec, Reactine, Triz, and Razene is a second-generation antihistamine which is used in the treatment of hay fever, allergies, urticaria and Angioedema. These second-generation antihistamines are not able to cross the blood–brain barrier and hence do not have much effect on the central nervous system, i.e. spinal cord and brain. For example they do not cause much drowsiness and memory disturbance like the first generation histamines.
The chemical name is [2-[4-[(4-Chlorophenyl) phenylmethyl]-1-piperazinyl] ethoxy]-acetic acid dihydrochloride
The 1-[(4-chlorophenylmethyl]-piperazine is alkylated with methyl (2-chloroethoxy)-acetate sodium carbonate, xylene solvent acts as a catalyst to produce the Sn2 substitution product in 28% yield. Then, saponification of the acetate ester is done by refluxing with potash in absolute ethanol to get a 56% yield of potassium salt intermediate. The last step is hydrolysis with aqueous HCl and extraction to get an 81% yield of the carboxylic acid product.
Adverse effects – common side effects include drowsiness (5–20%), headache (16%), dry mouth (5.7%), fatigue (5.6%), mood swings and irritability, nausea and vomiting, pain in abdomen, diarrhea.
Precautions – the drug must be prescribed with much caution in patients with hepatic or renal impairments, paediatric population, and geriatric population.
Pharmacokinetics – Cetirizine hydrochloride is available in chewable, non-chewable, and syrup forms and hence can be easily and effectively absorbed.