Aerosol therapy of asthma: principles and applications

Aerosols are the mainstay of therapy of reversible airflow obstruction. Currently available aerosols include bronchodilators such as beta-adrenoceptor agonists and anticholinergic agents which may be used alone or together with prophylactic, anti-inflammatory medications such as sodium cromoglycate and steroids. These agents are characterized by primarily topical activity and thus result in minimal systemic effects. By combining these medications in optimum doses, most patients can be readily managed. In patients with severe airway hyperreactivity, aerosols may need to be combined with oral sustained-release theophylline compounds and/or systemic steroids, the latter being used in minimum doses and if possible on alternate days to minimize adrenal suppression and steroid-related systemic complications. In recent years, an improved understanding of aerosol physics, pharmacology and airway physiology has led to greatly improved aerosol therapy with increasing emphasis on metered dose inhalers as the delivery system of choice while nebulizers are used less frequently except in hospital and pediatric applications. The use of intermittent positive-pressure devices for aerosol delivery has decreased considerably as physicians recognize that simpler delivery methods work equally well at much lower cost. While aerosol therapy techniques are now well worked out, research is continuing on methods of improving the efficiency of aerosol delivery and in the development of newer pharmacological agents such as longer-acting adrenoceptor agonists, calcium channel blockers, antagonists of mediators derived from arachidonic acid as well as higher dose aerosolized steroids.