Cetirizine hydrochloride, an antihistamine, is a major metabolite of hydroxyzine, and a racemic selective H₁ receptor inverse agonist used in the treatment of allergies, hay fever, angioedema, and urticaria. The structural similarity of cetirizine to hydroxyzine, and its derivation from piperazine, attribute similar adverse reactions and properties to other piperazine derivatives.

Formerly prescription-only in the US and Canada, cetirizine is now available over the counter in both.

Pharmacology

Cetirizine crosses the blood-brain barrier only slightly, eliminating the sedative side-effect common with older antihistamines; however is still causes mild drowsiness.

Administration method and metabolisation

Chewable, non-chewable, and syrup forms of cetirizine are similarly absorbed rapidly and effectively, with absorbed food minutely affecting the absorption rate which yields a peak serum level one hour after administration; in a study of healthy volunteers prescribed 10mg tablets, once daily for 10 days, a mean peak serum level of 311 ng/mL was observed. The metabolic effects of cetirizine are long acting; remaining in the system for a maximum of 21 hours before being excreted, the average elimination half-life is 8 hours. 70% of the drug is excreted or eliminated by kidney function within 72 hours, and 10% is removed through urine or excrement; of which, half is observed as unchanged cetirizine compound. Like many other antihistamine medications, cetirizine is commonly prescribed in combination with pseudoephedrine hydrochloride, a decongestant. These combinations are marketed using the same brand name as the cetirizine with a "-D" suffix (Zyrtec-D, Virlix-D, etc.)

Additionally, cetirizine HCl not sold in combination with pseudoephedrine, is commonly known and marketed in the United States under the brand name, "Zyrtec." Formerly only available by a prescription, both Zyrtec and Zyrtec-D are currently available over the counter in the United States. In the Philippines, a leading cetirizine is Aforvir.

Levorotary isomer

The levorotary enantiomer of cetirizine is known as levocetirizine. It is marketed under the name of Xyzal and Xusal. It is claimed to have somewhat fewer side effects.

Kimura's disease

Cetirizine is an effective agent in the treatment of Kimura's disease, which mostly occurs in young Asian men, affecting the lymph nodes and soft tissue of the head and neck in the form of tumor-like lesions. Cetirizine's properties of being effective both in the treatment of pruritus and as an anti-inflammatory agent make it suitable for the treatment of the pruritus associated with these lesions. In a 2005 study, the American College of Rheumatology conducted treatments initially using prednisone, followed by steroid dosages and azathioprine, omeprazole, and calcium and vitamin D supplements over the course of two years. The skin condition of the patient began to improve and the skin lesions lessened. However, there were symptoms of cushingoid and hirsutism observed before the patient was removed from the courses of steroids and placed on 10mg/day of cetirizine to prevent skin lesions;an agent suitable for the treatment of pruritus associated with such lesions. Asymptomatically, the patient's skin lesions disappeared after treatment with cetirizine, blood eosinophil counts became normal, corticosteroid effects were resolved, and a remission began within a period 2 months. It is also thought that the inhibition of eosinophils may be the key to treatment of Kimura's disease due to the role of eosinophils, rather than other cells with regards to the lesions of the skin.

References

Books and journals

1. Anderson, P. O., Knoben, J. E., et al. (2002) Handbook of clinical drug data 10th ed. McGraw-Hill International
2. Pfizer Inc, et al. (2006) ZYRTEC (cetirizine hydrochloride) Tablets, Chewable Tablets and Syrup For Oral Use Pfizer Incorporated publications
3. Chetrit, E. B., Amir, G., Shalit, M. (2005). Cetirizine: an effective agent in Kimura's Disease Arthritis & Rheumatism (Arthritis care & research) Vol 53, p117-118

External links

• Non-print version of cetirizine fact sheet.
• List of brand names
• US FDA approves Zyrtec-D for over the counter sales
• US FDA approves Zyrtec for over the counter sales