A dry powder inhaler is provided herein which includes a dose chamber having a staging area configured to accommodate an inhalable dose of active pharmaceutical agent. A nozzle is provided having a discharge aperture with an inhalation channel communicating the staging area with the discharge aperture. The inhalation channel is configured such that sufficient negative pressure applied to the discharge aperture draws a dose from the staging area towards the discharge aperture. An arrangement is provided for evaluating the level of depletion of a dose from the staging area. Advantageously, the subject invention allows for evaluating physical depletion of a staged dose so as to recognize the level of delivery thereof.
