Assessment methods of inhaled aerosols: technical aspects and applications

The pulmonary route has been used with success for the treatment of both lung (asthma) and systemic diseases (diabetes). The fate of an inhaled drug (absorption and deposition) within human lungs has great importance, particularly in drug development and quality control. This article focuses on the various methods that are now applied for aerosol fate investigation. Several assessment methods, ranging from in vitro assays (impaction and optical systems) to in vivo experiments (imaging and pharmacological methods), are described. In vitro assays measure particle size distribution and emitted drug dose, which could be predictive of lung deposition pattern in vivo. However, in vivo methods provide direct information about the concentration and the location of inhaled drug within lung. Advantages and limitations of the different techniques are identified. In addition to these experimental techniques, mathematical deposition models, elaborated in more realistic conditions and designed to predict the fate of inhaled particles, are also illustrated.