While realistic in vitro testing of dry powder inhalers (DPIs) can be used to establish in vitro–in vivo correlations (IVIVCs) and predict in vivo lung doses, the aerodynamic particle size distributions (APSDs) of those doses and their regional lung deposition remains unclear. Four studies were designed to improve testing centered on the behavior of Novolizer®. Different oropharyngeal geometries were assessed by testing different mouth-throat (MT) models across a realistic range of inhalation profiles (IPs) with Salbulin® Novolizer®. Small and large Virginia Commonwealth University (VCU) and Oropharyngeal Consortium (OPC) models produced similar ranges for total lung dose in vitro (TLDin vitro), while results for medium models differed significantly. While either group may be selected to represent variations in oropharyngeal geometry, OPC models were more difficult to use, indicating that VCU models were preferable. To facilitate simulation of human IPs through DPIs, inhalation profile data from a VCU clinical trial were analyzed. Equations were developed to represent the range of flow rate vs. time curves for use with DPIs of known airflow resistance. A new method was developed to couple testing using VCU MT models and simulated IPs with cascade impaction to assess the APSDs of TLDin vitro for Budelin® Novolizer®. This method produced IVIVCs for Budelin’s total lung dose, TLD, and was sufficiently precise to distinguish between values of TLDin vitro and their APSDs, resulting from tests using appropriately selected MT models and IPs. For example, for slow inhalation, TLD values were comparable in vivo and in vitro; TLDin vitro ranged from 12.2±2.9 to 66.8±1.7 mcg aerosolized budesonide while APSDs in vitro had mass median aerodynamic diameters of 3.26±0.27 and 2.17±0.03 µm, respectively. To explore the clinical importance of these variations, a published computational fluid dynamic (CFD) model was modified and coupled to accept the output of realistic in vitro tests as initial conditions at the tracheal inlet. While simplified aerosol size metrics and flow conditions used to shorten CFD simulations produced small differences in theoretical predictions of regional lung deposition, the results broadly agreed with the literature and were generally consistent with the median values reported clinically for Budelin.

This research was aimed at the development and validation of new in vitro methods capable of predicting in vivo drug deposition from dry powder inhalers, DPIs, in lung-normal human adults. Three physical models of the mouth, throat and upper airways, MT-TB, were designed and validated using the anatomical literature. Small, medium and large versions were constructed to cover approximately 95% of the variation seen in normal adult humans of both genders. The models were housed in an artificial thorax and used for in vitro testing of drug deposition from Budelin Novolizer DPIs using a breath simulator to mimic inhalation profiles reported in clinical trials of deposition from the same inhaler. Testing in the model triplet produced results for in vitro total lung deposition (TLD) consistent with the complete range of drug deposition results reported in vivo. The effect of variables such as in vitro flow rate were also predictive of in vivo deposition. To further assess the method’s robustness, in vitro drug deposition from 5 marketed DPIs was assessed in the “medium” MT-TB model. With the exception of Relenza Diskhaler, mean values for %TLD+SD differed by only < 2% from their literature in vivo. The relationship between inhaler orientation and in vitro regional airway deposition was determined. Aerosol drug deposition was found to depend on the angle at which an inhaler is inserted into the mouth although the results for MT deposition were dependent on both the product and the formulation being delivered. In the clinic, inhalation profiles were collected from 20 healthy inhaler naïve volunteers (10M, 10F) before and after they received formal inhalation training in the use of a DPI. Statistically significant improvements in Peak Inhalation Flow Rate (PIFR) and Inhalation Volume (V) were observed following formalized training. The shapes of the average inhalation profiles recorded in the clinic were found to be comparable to the simulated profiles used in the in vitro deposition studies described above. In conclusion, novel in vitro test methods are described that accurately predict both the average and range of aerosol airway drug deposition seen from DPIs in the clinic.