Effects of discoordination upon bronchodilator response to metered dose inhaler

Proper coordination of inhalation and MDI canister activation is an important determinant of availability of medication to airways and subsequent clinical response. We compared coordination to terbutaline and pirbuterol MDIs by evaluating clinical effects, deposition in a model of the human upper airway, rate of aerosol settling in a tank, and particle size distribution. The maximum clinical effects and least deposition in the upper airway occurred when both MDIs were activated at onset of inhalation. When MDIs were activated before inhalation, pirbuterol was less affected than terbutaline. Pirbuterol MDI aerosol is slightly smaller than terbutaline MDI aerosol. The results of this study strongly suggest that both clinical and airway model differences noted were due, at least in part, to smaller size of pirbuterol aerosol.