Azelastine is a novel antiallergy medication currently under investigation for the treatment of allergic rhinitis and asthma. Pharmacologic studies in laboratory animals and in vitro model systems indicate that azelastine exerts multiple actions including modulation of airways smooth muscle response, interference with inflammatory processes, and inhibition of allergic reactions. In a previous controlled clinical trial, azelastine nasal solution (ASTELIN N.S.) demonstrated effectiveness in controlling symptoms of seasonal allergic rhinitis (SAR). The objective of this 2-week double-blind, parallel-group study was to further assess the effectiveness of azelastine nasal solution in improving allergic rhinitis symptoms. Two hundred forty-seven patients (> or = 12 years) with symptomatic SAR who satisfied a minimum symptoms score during a 1-week, single-blind, baseline evaluation period were randomized to receive azelastine 2 sprays per nostril bid, azelastine 2 sprays per nostril qd, chlorpheniramine 12 mg bid, or placebo using a double-dummy technique to insure blinding. The primary efficacy variables were changes in Major Symptom Complex (nose blows, sneezes, runny nose/sniffles, itch nose, and watery eyes) and Total Symptom Complex (Major plus itchy eyes/ears/throat/palate, cough, and postnasal drip) severity scores. Patients treated with azelastine nasal solution qd and bid had mean percent improvements in the Total and Major Symptom Complex severity scores that were clinically significant (> or = 50% improvement over placebo) after both weeks, at endpoint, and overall. The improvements for the azelastine bid group were statistically significant (P < or = .05) at all evaluation points. Adverse experiences occurred infrequently, and none was considered serious or potentially limiting to the clinical utility of the nasal solution.(ABSTRACT TRUNCATED AT 250 WORDS)