Levocetirizine

Levocetirizine is an antiallergic agent belonging to the second-generation antihistamine class, used for the treatment of allergic conditions.‍​‍‍‍​‍‍‍‍‍‍‍‍​‍ It is the R-enantiomer of cetirizine with a higher affinity for the H1 receptor. Compared to first-generation antihistamines, it causes less fatigue and drowsiness, as it barely penetrates the brain. The onset of action is rapid and long-lasting, so that only one administration per day is sufficient. Levocetirizine (ATC R06AE09) has antihistaminic, antiallergic, and anti-inflammatory properties. It has a high selectivity for the histamine H1 receptor, is not anticholinergic, and is not cardiotoxic. It crosses the blood-brain barrier only to a negligible extent and therefore causes less fatigue and drowsiness than first-generation antihistamines; however, both adverse effects may still occur. The onset of action is rapid and long-lasting, so that it only needs to be administered once daily. Levocetirizine has a higher binding affinity for the H1 receptor compared to the S-enantiomer and dissociates more slowly. Mechanism of action of antihistamines, click to enlarge. Illustration © PharmaWiki