Blood Eosinophils: A Biomarker of Response to Extrafine Beclomethasone/Formoterol in Chronic Obstructive Pulmonary Disease
Authors: Salman H. Siddiqui, Alessandro Guasconi, Jørgen Vestbo, Paul Jones, Alvar Agusti, Pierluigi Paggiaro, Jadwiga A. Wedzicha, Dave Singh
Journal: American Journal of Respiratory and Critical Care Medicine (2015)

To the Editor:

Chronic obstructive pulmonary disease (COPD) is a heterogeneous condition (1). The identification of COPD phenotypes may allow stratified treatment approaches that modulate discrete disease mechanisms. Peripheral blood eosinophilia is both a common and repeatable finding in COPD (2). In addition, the presence of a blood/sputum eosinophilia is associated with a significant proportion of COPD exacerbations (3, 4) and a favorable response to systemic steroids (5). However, the role of blood eosinophils in stratifying treatment response to inhaled corticosteroid/long-acting β-agonist combinations is poorly understood.

The FORWARD (Foster 48-Week Trial to Reduce Exacerbations in COPD) study was a randomized, double-blind, parallel group trial that compared 48 weeks of treatment with extrafine beclomethasone dipropionate plus formoterol fumarate (BDP/FF), 100/6 μg pressurized metered-dose inhaler, two inhalations twice a day, versus FF 12 μg pressurized metered-dose inhaler, one inhalation twice a day, in patients with severe COPD with a history of exacerbations (clinical trial registered with www.clinicaltrials.gov [NCT 00929851]). The results of the study have been reported (6) and showed a significant reduction in exacerbation rate (28%) and improvement in lung function with BDP/FF compared with FF treatment.

Here we evaluate the hypothesis that these treatment differences differ according to the baseline blood eosinophil count by performing a post hoc analysis on the FORWARD study data.

Methods
The median (quartile 1; quartile 3) baseline blood eosinophil count was 181.6 (110.4; 279.8), and the distribution of counts is shown in Figure E1 in the online supplement. The patients (n = 1,184) were stratified into quartile groups on the basis of the baseline eosinophil count. The clinical characteristics of the study population across the quartiles of baseline blood eosinophils are reported in Table E1. The following endpoints were analyzed: COPD exacerbation rate over the course of 48 weeks, using a negative binomial model for adjusted exacerbation rates, Kaplan-Meier analysis, and Cox proportional hazard model for time to first exacerbation event; change from baseline in predose morning FEV1 at 48 weeks, using a linear mixed model for repeated measurements; and change from baseline in St. George’s Respiratory Questionnaire total score at 48 weeks, using an analysis of covariance model. Further details of the models are provided in the online supplement. Additional analyses using percentage eosinophil count thresholds and considering absolute counts as a continuous variable were also performed. A predictive model (see online supplement for details) for future COPD exacerbation rate was estimated, accounting for a variety of baseline factors that may influence exacerbations (7). The effect of baseline blood eosinophil count on adverse events, and in particular pneumonia, was also evaluated.