Summary
Flow profile studies are not explicitly mentioned in the OIP guideline[1], although most clinical development plans for generic dry powder inhalers (DPI) carefully enquire this aspect and its results. The reason is that the guideline implies the need for a study measuring inspiratory flow profiles. For the lack of a commercially available measuring device, Inamed developed a system according to several criteria.

The system was set up from components, which are commercially available and calibrated in a way that it allows to measure the pressure drop at the mouth piece of an inhaler as a function of time. The data had to be collected and converted into a flow rate as a subject inhales through a dry powder inhaler. The modification of the DPI does not alter the airflow resistance of the inhaler. The data is analysed for typical parameters like peak inspiratory flow rate or inhaled volume to generate output parameters for characterisation and comparison of the inhalation.
Based on a thorough validation and qualification our system has proven to be reliable in 4 clinical trials, with more than 400 patients. It has been used with various DPIs amongst them were Turbohaler and Diskus as well as one breath triggered device. The system can be used for both drug free studies with focus on the device and the handling itself or for studies with a drug delivery to the patient. Additionally this can be in combination with pk and scintigraphic deposition
studies.