Inhibition of mediator release during the early reaction to antigen.

A nasal lavage model and a new filter paper disk model have been used to measure biologic and physiologic responses to antigen challenge in patients with allergic rhinitis. Pretreatment of subjects with cetirizine reduced the number of sneezes induced by antigen challenge but did not significantly reduce levels of histamine or prostaglandin D2 in a double-blind, placebo-controlled trial with the lavage model. Pretreatment with 60 or 300 mg of terfenadine did significantly reduce levels of histamine, kinin, albumin, and TAME-esterase activity in a double-blind, placebo-controlled study with this model. Again with the nasal lavage model, a double-blind, placebo-controlled comparison of pretreatment with 60 mg of terfenadine or 10 mg of loratadine showed that both agents significantly reduced sneezing. Both drugs also lowered levels of antigen-induced histamine and TAME-esterase, but only terfenadine did so significantly. In a double-blind, placebo-controlled study, the new disk method showed that terfenadine reduced sneezing but not nasal congestion in eight patients with allergic rhinitis. Terfenadine significantly reduced the weight of nasal secretions on both sides of the nose and significantly reduced histamine on the ipsilateral side.