Major and minor criteria have been published in a consensus document to define this phenotype. In other guidelines, these patients are described as ‘patients with COPD and prominent asthmatic component’ or as asthma that complicates COPD. The mixed COPD–asthma phenotype was defined as an airflow obstruction that is not completely reversible accompanied by symptoms or signs of an increased reversibility of the obstruction. The Spanish COPD guidelines propose four COPD phenotypes that determine differential treatment: nonexacerbator with emphysema or chronic bronchitis, mixed COPD–asthma, exacerbator with emphysema and exacerbator with chronic bronchitis. Existing guidelines for asthma, such as the NIH, National Asthma Education and Prevention Program, Expert Panel Report 3, and COPD, such as both GOLD treatment guidelines and the consensus statement by the American College of Physicians, American College of Chest Physicians, ATS and European Respiratory Society, also do not fully capture the heterogeneity of asthma and COPD, including ACOS, nor do they prepare clinicians for the variable responses to pharmacotherapies, especially the burden of corticosteroid resistance. In clinical practice, separating asthma from COPD is difficult due to the overlapping features common to both diseases. However, a clinical definition is a necessary starting point for a review of potential pharmacotherapeutic approaches. An exploration of how best to define ACOS is beyond the scope of this article. COPD is a syndrome akin to asthma but with important differences, including tobacco smoke-induced pathobiology and pulmonary emphysema. Īsthma is a syndrome consisting of similar phenotypes with characteristic but nonspecific symptoms. Guidelines from Canada, Japan and Spain attempt to describe this clinical phenotype and establish treatment options. Asthmatic bronchitis was a term used to describe the overlapping conditions of asthma and COPD by the American Thoracic Society (ATS) in 1962, but no further attempts were made to expound on this clinical phenotype until recently. The asthma–chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) is poorly recognized in part because clinical trials have consistently ignored this condition, as evidenced by strict inclusion and exclusion criteria that exclude either asthma patients from COPD studies or COPD patients from asthma studies. A consensus international definition of ACOS is needed to design prospective, randomized clinical trials to evaluate specific drug interventions on important outcomes such as lung function, acute exacerbations, quality of life and mortality. The authors discuss the array of existing and emerging classes of drugs that could benefit those with ACOS and share their therapeutic approach. Pharmacotherapeutic considerations require an integrated approach, first to identify the relevant clinical phenotype(s), then to determine the best available therapy. Patients with ACOS have the combined risk factors of smoking and atopy, are generally younger than patients with COPD and experience acute exacerbations with higher frequency and greater severity than lone COPD. ACOS accounts for approximately 15–25% of the obstructive airway diseases and patients experience worse outcomes compared with asthma or COPD alone. Asthma–chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) is a commonly encountered yet loosely defined clinical entity.
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