A number of inhaled medications used to treat respiratory diseases (such as asthma and COPD) will soon be candidates for generic drugs due to the expiration of existing patents. If these drugs can be offered as generics, reduced costs may be possible while maintaining safety and efficacy, which will benefit consumers and the health care system. It has been suggested that low-cost pharmacokinetic (PK) studies, which monitor concentrations in the blood or urine, could be used to demonstrate equivalence. However, a better understanding of regional and local drug deposition patterns in the lung is required. The objective of this study is to advance the development of an existing CFD model of orally inhaled drug products that can account for inhaler characteristics (spray or air-jet momentum), drug physicochemical properties (aerodynamic size distribution, evaporation and condensation, dissolution) and physiological parameters (breathing pattern, geometry, disease state) on local and regional drug deposition throughout the airways. In a previous study (sponsored by the US FDA) the proposed CFD model accurately predicted mouth-throat (MT) and upper tracheobronchial (TB) deposition from commercial MDI and DPI inhalers, based on validation with concurrent in vitro experiments, and the model was demonstrated to predict drug deposition throughout the entire TB region. In this newly proposed study, the existing CFD model will be extended to predict deposition throughout the lungs (TB and alveolar regions) with the inclusion of wall motion. Models will be developed that can account for intersubject variability in terms of both geometry and inhalation waveforms. An emphasis of the current project will be on comparing both in vitro experiments and CFD predictions with available in vivo studies in terms of lung drug delivery and drug depositional distribution within the airways. To achieve this overall objective, the following specific aims are proposed.
Specific Aim 1 : Development and mesh generation of representative human airway geometries extending from the mouth-throat to the alveolar region Specific Aim 2: Development of characteristic geometries and inhalation conditions that can provide a range of parameters within which inter-subject variability can be assessed for a population Specific Aim 3: Simulation of transport and deposition of polydisperse DPI aerosols in the entire airways of healthy small, medium, and large subjects with different breathing patterns and assess intersubject variability Specific Aim 4: Simulation of transport and deposition of polydisperse drug particles in the entire airways of asthmatic patients with different breathing parameters The CFD model developed in this study will play a valuable role in the areas of inhaler design, selecting appropriate inhalation devices and inhalation flow conditions for optimal lung delivery, and determining bioequivalence between devices. Based on the previous first year of model development, interesting differences in the TB and alveolar delivery between standard MDI and DPI inhalers used with correct and incorrect inhalation profiles were demonstrated. Both the developed CFD model and in vitro tests will be extensively compared with in vivo data and will give researchers two methods for rapidly predicting drug distribution within the airways across a population. This new approach for determining drug deposition in the lungs coupled with low-cost PK data can ultimately be used to establish bioequivalence between generic and innovator products without the need for costly and difficult to interpret pharmacodynamic studies. In addition, the methods proposed are independent of therapeutic class and therefore would be applicable as a universal method for all orally inhaled drug products.
For generic drugs to be approved by the FDA as safe and effective, bioequivalence must be demonstrated with the innovator product. Establishing bioequivalence is currently difficult and expensive for inhaled medications, due to their local action within the lungs. This study develops a new computational fluid dynamics (CFD) model of pharmaceutical aerosol transport and deposition throughout the airways that can account for intersubject variability. The model is validated with concurrent laboratory experiments and existing clinical data on drug deposition in humans. It is proposed that the developed CFD model together with in vitro experimental tests can be used to replace expensive and difficult to interpret human subjects pharmacodynamic studies in establishing bioequivalence for inhaled medications.
