Effect of an inhaled antihistamine on exercise-induced asthma.

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Abstract
The ability of the H1 receptor antagonist clemastine to prevent exercise-induced asthma (EIA) was studied in 10 adult asthmatic [human] subjects. Exercise was performed for 8 min on a cycle ergometer on 2 occasions on each of 2 days, The 1st test each day was without premedication and the 2nd 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 1 s (FEV1). The 4 tests for each patient were closely matched in terms of O2 uptake and total ventilation, which were monitored throughout exercise. The response to exercise after clemastine or placebo was compared both directly and in terms of the degree of protection afforded against EIA compared to the initial test on the same day. Clemastine was significantly better than placebo for PEFR and FEV1. All 10 subjects had less EIA after clemastine, which suggests an important role for histamine in its production. Other mechanisms may be involved to a variable degree in different individuals.