Interactions between corticosteroids and β2-agonists

In vitro studies have demonstrated numerous ways in which β2-agonists and corticosteroids may interact. Together with evidence of improved control of airway diseases using a combination therapy of inhaled corticosteroids and long-acting β-agonists compared with treatment with either drug alone, this suggests that there may be a beneficial synergy between these two classes of medication. However, a positive interaction has not been clearly demonstrated in vivo. There is little evidence that β2-agonists enhance the anti-inflammatory actions of inhaled corticosteroids. Corticosteroids do not enhance the bronchodilator response to β2-agonists, nor do they appear to prevent the development of tolerance during chronic β2-agonist treatment. The evidence that high doses of corticosteroids can reverse tolerance to β2-agonists is conflicting. Most of the clinical benefits from combinations using inhaled corticosteroids and long-acting β-agonists to treat asthma could result from additive or complimentary effects of the drugs on different parts of the disease process. Nevertheless, there are several studies in which the combination of a long- or short-acting β-agonist with an inhaled corticosteroid appears to have provided more than additive clinical benefits. The issue warrants further study. Combined inhaled corticosteroid/ β-agonist treatment will remain the basis of asthma management for the forseeable future, and although the overall clinical benefit of the combination is no longer in doubt, there is more to learn about maximizing this benefit and minimizing adverse effects.