Overview of effects of theophylline.

Ever since xanthines were introduced into asthma therapy, more than 125 years ago, their therapeutic effectiveness has been explained as being due to extrapulmonary rather than, or in addition to, pulmonary drug actions. This article emphasizes that theophylline may have several potentially important effects in the lung. Theophylline relaxes the smooth muscle of large and small airways in humans and animals. Its relaxant effect is relatively independent of the type of mediator that constricts the airway. This suggests that functional antagonism, rather than specific pharmacologic mediator antagonism (e.g., adenosine antagonism), explains its bronchodilator effect. The consistent relaxant property of such xanthines as theophylline distinguishes these compounds from many other classes of established and experimental bronchodilator agents. Furthermore, many anti-inflammatory effects have been noted, suggesting that xanthines might be considered as prophylactic agents. Theophylline may not only attenuate the activity of stationary and blood-borne pulmonary inflammatory cells; it may also exert an anti-inflammatory action by directly affecting targets such as the epithelial lining (increasing the mucociliary transport rate) and the microvasculature (possibly reducing plasma exudation). The experimental anti-inflammatory pharmacology of theophylline is compatible with the observation that theophylline inhibits late pulmonary reactions in patients with atopic asthma and in sensitized animals challenged with allergen. The mechanism(s) of action behind the pulmonary actions of theophylline has not been assessed (neither phosphodiesterase inhibition nor adenosine antagonism may be involved). Central nervous system, gastroesophageal, renal, and metabolic actions of theophylline are briefly reviewed. Headache, nausea, and the relaxation of the lower esophageal sphincter can perhaps be classified as nonexcitatory and inhibitory effects in which the mechanism(s) of action is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)