Effect of an inhaled antihistamine on exercise-induced asthma.

The ability of the H1 receptor antagonist clemastine to prevent exercise-induced asthma (EIA) has been studied in 10 adult asthmatic subjects. Exercise was performed for eight minutes on a cycle ergometer on two occasions on each of two days. The first test each day was without premedication and the second was preceded by inhalation of 0.05% clemastine or saline placebo given single blind in random order. Ventilatory function was assessed by serial measurements of peak expiratory flow rate (PEFR) and forced expiratory volume in one second (FEV1). All four tests for each patient were closely matched in terms of oxygen uptake and total ventilation which were monitored throughout exercise. The response to exercise after clemastine or placebo has been compared both directly and in terms of the degree of protection afforded against EIA compared with the initial test on the same day. Clemastine was significantly better than placebo for both PEFR and FEV1. All 10 subjects had less EIA after clemastine, which suggests an important role for histamine in its production. Other mechanisms may also be involved to a variable degree in different individuals.