Bronchodilator effect of terbutaline aerosol is not affected by propellant vapour pressure or dose volume

A randomized, blind cross-over study was carried out in 12 patients with bronchial asthma to determine whether the bronchodilating effect of a metered dose inhaler was influenced by increasing the metering volume from 25 microliters to 50 microliters, or by increasing the vapour pressure from 374 kPa to 502 kPa. Spirometry, heart rate and tremor were recorded 15 min after terbutaline sulphate 31 micrograms, 63 micrograms, 125 micrograms, 250 micrograms, 2 X 250 micrograms and 5 X 250 micrograms. There was no significant difference in any of the variables recorded i.e. in forced expiratory volume in one second, forced vital capacity or in airflows when 50% and 25% of the FVC remained to be exhaled from the total lung capacity. It is concluded that the bronchodilating effect of a beta 2-agonist from a metered dose inhaler is not substantially affected by changes in metering volume or vapor pressure within the limits studied.