Therapeutic inhalation agents and devices. Effectiveness in asthma and bronchitis

Although a variety of therapeutic agents can be given as aerosols, the physical problems involved in delivering the drug to the peripheral airways have often been ignored. Therapeutic aerosols are deposited in the respiratory tract by two chief mechanisms--inertial impaction (in the oropharynx and in large conducting airways) and gravitational sedimentation (in small conducting airways and in alveoli). In practice, only about 10% of the aerosol dose reaches the lungs from metered-dose inhalers (MDIs) and nebulizers, and rather less from dry-powder inhalers. Changes in either aerosol particle size or inhalation mode can optimize the amount of aerosol delivered to the peripheral lung regions by each device. The inhaled route has several advantages over oral and intravenous administration for the treatment of asthma and bronchitis, ie, a rapid onset of drug action, a small drug dose, and a low incidence of systemic side effects. Although various disadvantages or problems have been proposed for the inhaled route, these seem to be of minor importance. Drugs inhaled from MDIs, dry-powder inhalers, or nebulizers are thought to be safe if used in the recommended manner.