Background: Levocetirizine is the active enantiomer of cetirizine, a potent drug with little metabolism widely used for allergic rhinitis and urticaria. Objective: This study compares the potency, consistency, onset, and duration of action of levocetirizine with other popular antihistamines. Methods: Levocetirizine 5 mg, ebastine 10 mg, fexofenadine 180 mg, loratadine 10 mg, mizolastine 10 mg, or placebo in single doses were given to 18 healthy male volunteers in a double-blind, crossover, randomized fashion. Wheal-and-flare responses to epicutaneous histamine dihydrochloride (100 mg/mL) challenge were measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 hours after each dose. Results: The overall effect of each drug was evaluated by the area under the curve (0 to 24 hours). Levocetirizine was the most potent and consistently effective drug for inhibiting the histamine-induced wheal-and-flare surface areas. Ebastine, fexofenadine, and mizolastine ranked next and had almost identical effects for inhibiting the wheal. Loratadine was the least potent drug. Levocetirizine, fexofenadine, and mizolastine inhibited the wheal-and-flare response after 1 hour and reached their peak for inhibition after 4 hours. Ebastine and loratadine could be distinguished from placebo only after 4 hours. After treatment with levocetirizine, all 18 subjects had >95% inhibition of the wheal response at one timepoint. Fexofenadine, mizolastine, and ebastine were inhibitory in declining order. All treatments were considered safe and well tolerated. Conclusions: Levocetirizine, the active enantiomer of cetirizine, is more potent and consistent than other popular H-1 antihistamines for blocking the cutaneous response to histamine. These findings may predict the efficacy of this drug in treating allergic disorders.
