In vivo and ex vivo inhibitory effects of loratadine on histamine release in patients with allergic rhinitis

Background The aim of this study was to evaluate the in vivo and ex vivo ef fects of the H-1-antagonist loratadine on histamine release. Methods The study was designed as a double-blind, crossover trial. Ten pati ents with allergic rhinitis due to Dermatophagoides pteronyssinus were trea ted with Ioratadine (10 mg daily p.o.) and with placebo for 1 week, with a 2-week interval between the two treatments. Nasal lavages with saline solut ion were done before and after challenge with the relevant allergen at the end of treatments with loratadine and placebo. Venous blood was taken after treatments; and basophil histamine release induced by anti-IgE (10 mu g/ m l), N-formyl-methionyl-leucyl-phenylalanine (fMLP, 1 mu M), and Ca2+ ionoph ore A23187 (1 mu M) was evaluated by an automated fluorometric method. Results Treatment with loratadine attenuated early antigen-induced nasal ob struction, rhinorrhea, and itching. Nasal symptoms were accompanied by a si gnificant histamine release in the nasal lavages collected 5 min after stim ulation when the patients received placebo (median 4 ng/ml, range 1-28; P<0 .05). After treatment with loratadine, histamine release in the 5-min postc hallenge lavages was almost abrogated (median 0.5 ng/ml, range 0-3; P< 0.01 vs placebo). Median anti-IgE-induced histamine release from basophils was 41.9% (range 27.8-79.2) after placebo and 30.0% (range 1.7-73.3, P < 0.05) after loratadine. Active treatment exerted an inhibitory effect also on bas ophil histamine release induced by fMLP and Ca2+ ionophore A23187. Conclusions Treatment for 1 week with loratadine reduces allergen-induced n asal symptoms and inhibits in vivo and ex vivo histamine release in patient s with allergic rhinitis.