Why Target Drug Delivery to Small Airways?
Small-airway disease is a significant component of obstructive airway pathology. Emphysema classically involves the terminal bronchioles, but increasingly there is recognition that asthma, and in particular chronic persistent asthma, also involves the small airways (3). A variety of other lung diseases, including bronchiectasis, extrinsic allergic alveolitis, and sarcoidosis also involve the small airways. Current metered-dose inhalers (MDIs), pressurized inhalers, or dry-power inhalers (DPIs) are not very efficient at specifically depositing medication in the more peripheral airways of the lung. In many patients it is more effective to use oral medication. Mechanisms of Particle Deposition in the Airways There are three main ways in which particles become deposited in the lung: inertial impaction, sedimentation, and diffusion. Inertial impaction tends to occur in the upper airways when the velocity and mass of the particles cause them to impact the airway surface. For this reason, ine