Aerosol therapy is a complex process that depends on nebulizer performance and patient features. In order to avoid errors, these variables should be studied separately. The amount of drug within the respirable range is an objective parameter to quantify the amount of drug available at the end of the spacer system and potentially capable of reaching the lower airways. This simple method has been suggested to standardize first-step aerosol therapy delivery3 and is currently the only way of assessing the effective amount of drug administered. Moreover, if comparative in vitro determination does not show equivalence, it is highly likely that either will clinical comparison. If pMDI drugs are to be used with different spacers, instructions must be given about how to make the same effective amount of drug to be administered available at the end of each spacer. Our results were supported by statistical analysis, particularly a general linear model for repeated measures using type of treatment and sex as factors and age as covariate. FEV1 (F = 28.733; P < .001) and peak expiratory flow (F = 25.879; P < .001) were shown to increase significantly after both treatments.