Blood eosinophils are a promising biomarker to predict the therapeutic response to inhaled corticosteroids in patients with COPD, research suggests.

The post- hoc analysis of data from two double-blind, randomised placebo-controlled trials compared fixed combination of inhaled corticosteroids (fluticasone furoate at three doses, 50, 100, and 200 μg) and a long-acting β-agonist (vilanterol at 25 μg) with monotherapy with vilanterol (at 25 μg) in patients with moderate-to-severe COPD and a history of at least one exacerbation in the previous year.

According to an accompanying editorial by respiratory experts from Belgium and The Netherlands the authors made three important observations.

First, in the vilanterol alone group, the annual exacerbation rates increased progressively with increasing blood eosinophil counts as measured at baseline: the number of exacerbations per patient per year was 0·89 (for blood eosinophil count <2%), 1·21 (for 2 to <4%), 1·24 (for 4 to <6%), and 1·62 (for ≥6%) in patients with COPD.

“This dose-dependent increase in exacerbation rates with increasing blood eosinophil counts clearly indicates that blood eosinophils are a prognostic marker in COPD,” they wrote in the Lancet Respiratory Medicine. 

Second, compared with the vilanterol monotherapy group, combination therapy decreased annual exacerbation rates by 29% in patients with blood eosinophil counts equal or higher than 2%, but only by 10% in patients with blood eosinophil counts lower than 2%.

Finally, whereas the two original randomised trials confirmed the increased risk of pneumonia in patients treated with fluticasone furoate plus vilanterol compared with vilanterol alone (3·0% vs 1·0%), the pneumonia rates in patients treated with fluticasone furoate plus vilanterol seemed to be independent of blood eosinophil count.

“However, in patients receiving vilanterol alone, the investigators made the intriguing observation that rates of pneumonia were higher in the group with blood eosinophil counts lower than 2% compared with the group with counts equal to or higher than 2%,” they wrote.

The “landmark” study suggests that blood eosinophil counts are an important prognostic biomarker in COPD (ie, the risk of exacerbations is significantly increased in patients with high blood eosinophils, and the risk of pneumonia is highest in patients with eosinopenia) and that blood eosinophil counts predict the therapeutic response to inhaled corticosteroids, they concluded.

“If these important findings are confirmed and validated, we will finally have a method to target the use of inhaled corticosteroids to those patients with COPD who will benefit the most, improving the currently modest benefit–risk ratio,” they said.

The study was sponsored by GlaxoSmithKline.