Randomised controlled trials (RCTs) that compared long-acting beta2-agonists (salmeterol or formoterol) with placebo, or compared a combination of long-acting beta2-agonists plus inhaled corticosteroids with inhaled corticosteroids alone, in children or adults diagnosed with asthma, were eligible for inclusion. Trials were required to report change in an inflammatory marker as a primary outcome. Relevant markers were detailed for the large airways, small airway and tissue. Trials where inflammation was induced by a controlled allergen were excluded.
The included trials evaluated the anti-inflammatory effect of long-acting beta2-agonists versus placebo, or long-acting beta2-agonists plus inhaled corticosteroids versus inhaled corticosteroids alone. Trial designs included parallel and crossover. Inflammatory markers reported included cell counts, markers of cell activation in sputum, bronchoalveolar lavage fluid, bronchial biopsy specimens, serum and exhaled nitric oxide. The duration of the trials ranged from one to 52 weeks.
Studies were selected by two independent reviewers; it was unclear how disagreements were resolved.