EFFECTS OF H-1 AND H-2 ANTIHISTAMINES ON HISTAMINE INHALATION CHALLENGES IN ASTHMATIC-PATIENTS

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Abstract
The effect of an H1 antihistamine, chlorpheniramine [CP], an H2 antihistamine, cimetidine [CM], and the combination of CP and CM on histamine-induced bronchoconstriction in a double-blind, randomized protocol on 11 patients with asthma was examined. 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 CP, 300 mg of CM, the combination of CP and CM, 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 1 s, 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 CP (P < 0.002) and decreased after administration of CM (P < 0.02), but no significant effect was noted after the combination of CP and CM. Both H1 and H2 receptors are apparently present in the airways of asthmatic patients.