Am. J. Respir. Crit. Care Med.,
Volume 165, Number 8, April 2002, 1068-1070
2-Agonist Tolerance and Exercise-induced
Bronchospasm
Robert J.
Hancox,
Padmaja
Subbarao,
Dennis
Kamada,
Richard M.
Watson,
Fredrick E.
Hargreave,
and
Mark D.
Inman
Asthma Research Group, Firestone Institute for Respiratory Health, McMaster University/St Joseph's Hospital, Hamilton, Ontario, Canada
The effect of regular inhaled 
-agonist on the treatment of exercise-induced bronchoconstriction was studied. Eight subjects with
exercise-induced bronchoconstriction took 1 week each of salbutamol 200 µg qid or placebo in a random-order, double-blind, crossover study. They then withheld this treatment for 8 hours before
performing a dry-air, sub-maximal exercise challenge at a work-rate previously shown to induce a 15% fall in forced expiratory volume in 1 second (FEV1). Five minutes after exercise, they inhaled salbutamol 100, 100, and 200 µg at 5-minute intervals. The
mean pre-exercise FEV1 was similar on both study days. However,
pretreatment for 1 week with salbutamol led to a significantly
greater fall in FEV1 after exercise. The FEV1 remained lower than
during the placebo arm despite the administration of salbutamol
after exercise. This difference persisted 25 minutes after exercise.
It is concluded that regular -agonist treatment leads to increased
exercise-induced bronchoconstriction and a suboptimal bronchodilator response to -agonist. The data suggest that previous regular -agonist treatment may lead to a failure to respond to emergency bronchodilator treatment during an acute asthma attack
and support current opinion that regular short-acting -agonist
therapy should not be used to treat asthma.
