13 - Aerosols and Drug Delivery

Abstract

An aerosol can be defined as a system of solid particles or liquid droplets that can remain dispersed in a gas, usually air. Therapeutic aerosols contain a wide range of particle sizes. The aerodynamic behavior of an aerosolized particle is critically dependent on the size distribution of aerosolized particles. Therapeutic aerosols can be generated in three common ways: micronized dry powder, micronized particles suspended in a volatile pressurized liquid, or droplets generated by a dispersal force applied to a liquid. Some aerosol devices are designed to be coordinated with inspiration to increase the efficiency of drug delivery. In devices that generate aerosol throughout the respiratory cycle, a significant proportion of drug will be wasted during the expiratory phase, especially in children with low minute ventilation. When a drug is inhaled, fractions of the inhaled dose will deposit in the upper airway, the ciliated airways, and the alveoli, and a fraction can be exhaled. The resulting deposition pattern will be affected by the aerodynamic characteristics of the aerosol, the breathing pattern, and the airway anatomy. The total dose of an aerosolized drug that deposits in a patient is a function of the output of the device that generates the aerosol and the cumulative amount of inhaled drug that deposits in the upper and lower airways. The presence of airway or parenchymal disease can have a major impact on inhaled drug delivery, and drug/device combinations need to be customized for specific conditions and patient groups. Radiolabeled aerosols can be used to measure drug deposition patterns and mucociliary clearance.