Effects of divided doses of a bronchodilator aerosol and the intervening time interval on the forced expiration.

Twelve patients with bronchial asthma participated in a blind, randomized, crossover study comparing the effects of 500 micrograms terbutaline in one inhalation, 125 micrograms in four inhalations taken in rapid succession, and 125 micrograms in four inhalations taken with an intervening time interval of 30 min. There were no significant differences between the three modes of inhalation of 500 micrograms terbutaline in any of the spirometric variables, i.e., 1-second forced expiratory volume, forced vital capacity, and maximal airflows when 50 and 75% of the forced vital capacity was exhaled from the total lung capacity. However, there were neither any significant differences between the levels of bronchodilation reached after administration of 500 micrograms and 2 or 3 X 125 micrograms terbutaline with an intervening time interval of 30 min. The time interval between the divided doses was possibly too long to achieve maximum accumulated effect of the four divided doses.