The effects of H1 and H2 antihistamines on histamine inhalation challenges in asthmatic patients

This study was designed to examine the effect of an H1 antihistamine, chlorpheniramine, an H2 antihistamine, cimetidine, and the combination of chlorpheniramine and cimetidine on histamine-induced bronchoconstriction in a double-blind, randomized protocol on 11 patients with asthma. Each patient underwent a histamine inhalation challenge on 5 separate days. After a control day, histamine inhalation challenges were performed 2 h after the administration of a single oral dose of 8 mg of chlorpheniramine, 300 mg of cimetidine, the combination of chlorpheniramine and cimetidine, or placebo. Baseline pulmonary function measurements were not significantly altered by the 4 treatments. Body plethysmography data and measurements from the forced vital capacity maneuver were obtained before and after the histamine inhalation challenges. The provocation dose of histamine that produced a 20% decrease in forced expiratory volume in one second, a 35% decrease in mean forced expiratory flow during the middle half of the forced vital capacity, and a 50% decrease in specific airway conductance was significantly increased after administration of chlorpheniramine (p less than 0.002) and decreased after administration of cimetidine (p less than 0.02), where as no significant effect was noted after the combination of chlorpheniramine and cimetidine. The results suggest the presence of both H1 and H2 receptors in the airways of asthmatic patients.