[Bronchodilators]

Abstract

Bronchodilating drugs can be divided into three main groups: beta-adrenergic stimulants including specific beta-2 receptor agonists (salbutamol, terbutaline, fenoterol) which are the agents of this group used in everyday practice, theophylline and its derivatives, and atropine-like drugs (ipratropium bromide). Bronchodilators act chiefly upon the spasm observed at the bronchial level in reversible obstructive phenomena (mainly asthma), their effect upon inflammation and hypersecretion being slight or controversial. Beta-stimulants have a relatively specific mode of action at the bronchial level in the setting of use in pneumology; they exhibit cardiac effects only at high doses and when used by oral or parenteral routes. Relative to isoprenaline, they also have the advantage of being active orally and over a longer period of time. They are given in maintenance treatment of asthma, by parenteral or oral routes or as aerosols. Main side effects of adrenergic beta-stimulants are tremor with oral administration, and tachycardia with very high doses by parenteral or oral routes; when given as aerosols these agents may fail to control severe attacks. The bronchodilating properties of theophylline have been known for a long time; late advances concerning this drug result from better knowledge of its pharmacokinetics. Recent studies have discriminated between serum levels correlated with therapeutic effectiveness and those accompanied with mild or severe side effects; in addition, it has been clearly shown that the half life of this alkaloid varies from one person to another and with various physiopathologic (age, dietary habits, liver failure, heart failure...) or pharmacologic (drug interactions with enzyme inductors or inhibitors...) factors; these recent advances have led to improved individual adjustment of theophylline dosage using serum concentration assays if needed. Theophylline is used in acute attacks and in maintenance therapy of asthma. Main side effects are digestive intolerance and, with toxic doses, neurologic disorders. Atropine-like drugs inhibit the effects of the parasympathetic reflex which results from stimulation of receptors by irritation of the respiratory tract, through the action of mediators. In this group, ipratropium is the only drug given in aerosols; this, together with its pharmacologic specificity, contributes to its tolerance. In some instances, the bronchodilating effect of ipratropium bromide is comparable to that of sympathomimetics.