Levocetirizine is the active enantiomer of cetirizine. It is inverse agonist of H1 receptors. Levocetirizine hydrochloride was approved for treatment of Allergic Rhinitis and Chronic Idiopathic Urticaria.

Cetirizine, a human metabolite of hydroxyzine, is an antihistamine; its principal effects are mediated via selective inhibition of peripheral H1 receptors. It is indicated for the relief of nasal and non-nasal symptoms associated with seasonal or perennial allergic rhinitis, hay fever and chronic idiopathic urticaria. Commonly reported adverse reactions of cetirizine include headache, dry mouth and drowsiness or fatigue. Pharmacokinetic interaction studies with Cetirizine in adults were conducted with pseudoephedrine, antipyrine, ketoconazole, erythromycin and azithromycin. No interactions were observed.