Airway-stabilizing effect of long-acting 2-agonists as add-on therapy to inhaled corticosteroids

Background:  The protection afforded by long-acting β2-agonists against bronchoconstrictor stimuli can be regarded as a surrogate for their stabilizing effects on airway smooth muscle. Aim:  To determine the magnitude of residual bronchoprotection after chronic dosing with long-acting β2-agonists. Design:  Retrospective meta-analysis Methods:  Medline, BIDS and Cochrane Library databases were searched from 1990. A meta-analysis was then performed of 13 eligible randomized placebo-controlled trials (596 patients) in which second-line treatment with a long-acting β2-agonist (salmeterol or formoterol) was used for 1 week or more. The residual protection against bronchoconstrictor stimuli as doubling dose/dilution shift was the main outcome measure. Results:  Data were assessed according to Quorum criteria. Combining the results of the meta-analysis, the overall estimated protection amounted to a 0.79 (95%CI 0.63–0.96) doubling dose/dilution shift from placebo. Subgroup analysis showed greater protection at peak vs. trough, but no difference between formoterol vs. salmeterol, or between direct vs. indirect challenge. There was no evidence of significant heterogeneity across all the studies, or within any of the subgroups. Discussion:  When used as second-line treatment, the overall additive protective effect of long-acting β2-agonists amounts to a 0.8 doubling dose/dilution shift. This stabilizing effect on airway smooth muscle may explain their beneficial effects on exacerbations.