The widespread use of aerosol therapy in the treatment of pulmonary diseases is based on optimizing drug properties and aerodynamic behavior of airborne particulates. In order to understand drug properties and aerodynamic behavior, it is important to recognize that each category of inhaler delivers a product with different physicochemical characteristics, and that these properties determine the site of deposition and the mechanism of clearance from the lungs. The complex interplay of these properties and the physiology and anatomy of the lungs must be considered to fully understand the implications for drug delivery. The aerodynamic behavior of aerosols under various inspiratory flow conditions influences the site of deposition. Once the particle comes to rest in the lungs, mechanisms of clearance are invoked, including dissolution and absorption, or, for more insoluble materials, mucociliary transport or cell-mediated transport. Finally the pharmacokinetics of drug disposition dictate the pharmacodynamic effects of the drugs responsible for efficacy
