Levocetirizine: the allergist's arsenal grows larger.

Antihistamines are the cornerstone of treatment for many allergic diseases, such as allergic rhinitis and chronic urticaria. Since the discovery of their beneficial effects in the 1940s, scientists have found molecules with greater selectivity to block specific histamine receptors without some of the detrimental side effects that are seen if antihistamines cross the blood-brain barrier. Levocetirizine is the active enantiomer of cetirizine and a selective H(1)-histamine blocker. It exhibits many favourable characteristics of an ideal antihistamine, both pharmacodynamically and pharmacokinetically, including high bioavailability, rapid onset of action, limited distribution and low degree of metabolism. Furthermore, clinical trials indicate that it is safe and effective for the treatment of allergic rhinitis and chronic urticaria with a minimal amount of untoward effects.