The effect of a beta 2-adrenergic agonist and a histamine H1-receptor antagonist on the late asthmatic response to inhaled antigen.
In this double-blind, randomized, cross-over trial, the role of histamine and the possible protective effect of a beta 2-adrenergic agonist in the later asthmatic response to inhaled antigen was investigated in nine atopic asthmatic patients. On four study days, 2-4 weeks apart, patients were given either: placebo; salbutamol aerosol 400 micrograms before and 200 micrograms 2-hourly after challenge; oral terfenadine 120 mg 2 h before and 10 h after challenge; and, on the final day, lung function was monitored without medication or antigen challenge. A nebuliser-dosimeter system was used to deliver a predetermined, single dose of antigen aerosol. Response was assessed by specific airways conductance (SGAW) measured in a body plethysmograph; FEV1 and PEFR were measured with a Pocket Spirometer. All measurements were made for 10 h in the clinic and then the patients continued to record PEFR and FEV1 at home for at least 2 more hours. Similar findings were obtained with all three lung function parameters. After challenge, the early response (ER) was small when compared with the late response (LR). All patients had a definite LR on the placebo day when FEV1 was compared with 'no challenge day'. Neither drugs had much effect on the small ER. The LR was not altered by terfenadine but was very significantly attenuated by salbutamol; the mean maximum fall in FEV1 during LR being 31, 29 and 12% after placebo, terfenadine and salbutamol, respectively. It is unlikely that histamine plays an important role in the LR to inhaled antigen but beta 2-adrenergic stimulants can attenuate LR, probably by directly preventing bronchial smooth muscle constriction and also by stabilising bronchial mast cells.