Influence of an extension tube on the bronchodilator efficacy of terbutaline delivered from a metered dose inhaler.

Pressurized aerosols of sympathomimetic drugs are widely used in the treatment of bronchial asthma. The efficacy of this form of treatment is diminished in a number of patients by difficulties in coordination between the aerosol actuation and the inhalation. In order to improve the intrapulmonary deposition of terbutaline, an extension tube has been adapted to the regular pressurized aerosol device. In a cross-over randomized study we compared the bronchodilatory effect of increasing doses of terbutaline (250, 500 and 750 micrograms at 25-min intervals) either delivered by the regular pressurized aerosol device or by the device with the extension tube. The study was performed on 11 adult patients with reversible airways obstruction. Spirometry, body plethysmography and flow volume curves were performed. The onset of the bronchodilatory effect of a single dose of 250 micrograms terbutaline was more rapid after delivery via the extension tube. The addition of the extension tube caused a significantly higher bronchodilator efficacy of aerosolized terbutaline on the small airways. Our results show that the addition of an extension tube improves the bronchodilator efficacy of terbutaline delivered from a pressurized aerosol.