Asthma treatment: inhaled beta-agonists.
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Short acting beta-agonists provide symptom relief with a rapid onset of bronchodilation, and protect against exercise-induced asthma and the early asthmatic response to allergen. They remain the most commonly prescribed form of therapy in asthma. However, regular use as maintenance therapy for chronic asthma is no longer recommended. Frequent use increases airway hyper-responsiveness to allergen and nonspecific challenge, and in some studies has been associated with decreased control of asthma. Excessive use of short acting beta-agonists is associated with a higher risk of fatal or near-fatal asthma, with a dose-response relationship. High doses of short acting beta-agonist in combination with oxygen and corticosteroid therapy remains the most appropriate treatment for acute severe asthma in the emergency room situation. The long acting beta-agonists salmeterol and formoterol provide more prolonged bronchodilation, greater reduction of symptoms, increased lung function and reduced need for short acting beta-agonists. Although there is no significant tachyphylaxis to the bronchodilator effects, bronchoprotective effects diminish with time, even when patients are also treated with corticosteroids. The concern that long acting beta-agonists may mask inflammation and, hence, increase the risk of exacerbations was addressed in a recent four-arm parallel group study. The exacerbation rate was highest in those receiving low dose corticosteroid and was progressively lower in those with low dose corticosteroid plus formoterol, moderate dose budesonide alone and moderate dose budesonide plus formoterol. Both budesonide and formoterol independently decreased the risk of exacerbations. Short acting beta-agonists are recommended for use only as needed, which should be relatively infrequent. Long acting beta-agonists are indicated in individuals whose asthma is not well controlled on moderate doses of inhaled corticosteroid, and are complementary to, not a replacement for, inhaled corticosteroid therapy.
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