Long-acting inhaled β₂-agonists in asthma therapy

Objective: To review the pharmacology of the long-acting inhaled β₂- agonists, salmeterol and formoterol, summarize results of their clinical trials, evaluate their safety records, and discuss their roles in the treatment of asthma. Data sources: Preclinical and clinical studies involving salmeterol or formoterol were identified by a MEDLINE search, weekly computerized literature updates, and manual searches. Studies of satisfactory quality were chosen for review. Data synthesis: Salmeterol and formoterol are potent and selective β₂-adrenoceptor agonists with durations of action > 12 h. Their major differences are that formoterol has a rapid onset of action and is a partial agonist of high intrinsic efficacy, whereas salmeterol has a delayed onset and is a partial agonist of low intrinsic efficacy. Twice daily use of either drug results in improved lung function, reduced symptoms, and a better quality of life. These agents protect against exercise-induced asthma for 12 h and eliminate nighttime awakening in most patients. Limited tolerance develops, especially to their bronchoprotective effects, but their improvement of lung function is sustained. Conclusions: Regular use of salmeterol or formoterol provides subjective and objective amelioration of asthma in patients experiencing excessive symptoms or physiologic impairment despite the regular administration of low doses of inhaled corticosteroids (equivalent to approximately 500 μg/d of beclomethasone). Intermittent use of either long-acting β₂-agonist can provide prolonged protection against exercise-induced asthma or nighttime symptoms. Patients should be instructed to continue taking inhaled steroids when long-acting β₂-agonists are administered on a regular schedule and to not take long-acting β₂-agonists between regularly scheduled doses. Used properly, they are effective and safe adjunctive agents in the treatment of asthma.