Comparison between nasal provocation tests and skin tests in patients treated with loratadine and cetirizine

Background: The effect of H1-blockers may differ depending on the target organ. Objective: A double-blind, placebo-controlled study was carried out to compare the effect of a 7-day treatment with loratadine (10 mg daily) or cetirizine (10 mg daily) on nasal challenge with grass pollen grains and skin tests with allergen or histamine. Methods: Twenty-four patients were enrolled, but the analysis was carried out on 23. Nasal challenge was carried out by using 5-fold increasing numbers of pollen grains. Skin prick tests were done with serial concentrations of allergens and 1 concentration of histamine. Patients were tested in a cross-over design, with each treatment being administered for the previous 7 days and with a 2-week washout period. Results: By comparison with placebo, loratadine and cetirizine increased significantly the threshold number of pollen grains required to induce a positive nasal challenge ( P < .001). There was no difference between loratadine and cetirizine. Skin test responses to allergen were significantly reduced by loratadine and cetirizine by comparison with placebo. Skin test responses to histamine were significantly decreased by the 2 H1-blockers, but they were more profoundly decreased by cetirizine than by loratadine. Conclusions: Both H1-blockers reduced similarly allergen-induced skin test and nasal challenge responses. Cetirizine was more effective on histamine skin test responses. (J Allergy Clin Immunol 1999;103:591-4.)