Single-dose dry powder inhalation devices involve the use of a capsule containing the drug that must be perforated for inhalation. This capsule can be transparent or opaque, which can be essential when generating positive visual feedback. To date, studies comparing these single-dose devices do so in terms of bioequivalence, but the feedback resulting from the transparency of the capsule has not been evaluated.

Our objective is to check if the use of a transparent capsule ensures a lower residual deposit thus generating a positive visual feedback.


This is an observational cross-sectional study including patients on active treatment with a single-dose dry powder inhaler. Patients with experience and good adherence in the use of this therapy were selected for the trial.

The capsule was weighed before and after inhalation with a high-precision microbalance and the weight change before and after inhalation between the opaque capsule and the transparent one was calculated and expressed in mg. In case the patient considered under his own criteria that he had not made the taking correctly, he was allowed to take a second inhalation.


A total of 56 patients participated in the present analysis, of whom 55.4% were men and the mean age was 67 years. There was a 26.8% of patients users of dry powder inhaler with opaque capsule, while the rest used transparent capsule. The evaluation of weight change revealed statistically significant differences with less residual weight for the transparent capsule.


Single-dose dry powder inhalation devices using a transparent capsule achieve a lower residual weight suggesting greater drug inhalation.