Bronchodilatation after inhalation of the antihistamine clemastine.
H1 receptor blocking antihistamines administered by mouth have not found a clear place in the management of bronchial asthma. We investigated the possibility that higher concentrations of these drugs, administered directly to the bronchial tree, might produce bronchodilatation. Twelve asthmatic patients inhaled aerosols generated from solutions of clemastine (0.05%), salbutamol (0.5%), and placebo. Bronchodilatation was assessed by changes in the forced expiratory volume in one second (FEV1) and peak expiratory flow rate (PEFR) over four hours. Both clemastine and salbutamol caused significant bronchodilatation. The mean maximum percentage increases in FEV1 for clemastine and salbutamol were 21.1% and 29.2% respectively. The mean maximum percentage increases in PEFR were 31.2% and 35.2% respectively. There was no significant difference in the maximum bronchodilatation produced by the two drugs. Clemastine, when administered by aerosol inhalation, appears to be an effective bronchodilator.