A magnet-based capsule rotation tracking for assessing inhalation success in dry powder inhalers

Dry powder inhalers (DPIs) provide important therapy options for the treatment of airway diseases. It is widely reported that the success of an inhalation maneuver depends not only on the properties of the formulation and the device, but also on the patients' ability to apply the inhaler as intended. An insufficient duration of the inhalation maneuver or an insufficient inspiration force might lead to an unfavorable therapeutic outcome. To counteract this problem, the study demonstrates feasibility of a new feedback system for RS01-type DPI devices aiding to assess the quality of the inhalation maneuver. Capsules have been modified to hold a neodymium magnet permitting to induce electric currents into an adjacently placed coil when rotating. The voltage induced was recorded and profiles obtained were shown to contain information about the duration flow rate applied during the actuation. Number of capsule revolutions and the overall volume (R² = 0.9991), as well as the applied flow rate and the frequency for the Cyclocaps® formulation (R² = 0.9893) were positively correlated when investigated under in vitro conditions using linear flow profiles. Through adequately characterizing a formulation with the new system and then linking the obtained fraction of the emitted mass with an aerodynamic diameter < 5 µm to the mentioned feedback variables, predictions can be made about the inhalation quality as well as the amount of respirable particles inhaled.