Comparison of the potency of antihistamines

First- and second-generation antihistamines have proven effective in the management of patients with urticaria and allergic rhinitis; however, the efficacy of first-generation antihistamines has been compromised by undesirable side effects such as sedation, dry mouth, and blurred vision. Second-generation antihistamines, on the other hand, are less sedating and have fewer side effects than first-generation agents. Recently second-generation agents have been compared for their pharmacologic activities using an epicutaneous histamine-induced wheal and flare model in normal volunteers. Cetirizine was found to be superior to epinastine, ebastine, fexofenadine, terfenadine, loratadine, and placebo in inhibiting the wheal and flare response. Epinastine had the fastest onset of action at 30 minutes and terfenadine proved to be superior to its metabolite fexofenadine.