Impact of long-acting muscarinic antagonists on small airways in asthma and COPD: A systematic review

Small airway disease is recognized as a cardinal pathological process of chronic obstructive pulmonary disease (COPD), and recently small airways have been recognized as a major site of airflow obstruction also in asthmatic patients. The transversal involvement of small airways in COPD and asthma has warranted research efforts to identify therapeutic strategies able to unlock the small airway compartment. The mainstay of COPD treatment is represented by long-acting beta(2)-adrenoceptor agonists (LABAs) and long-acting muscarinic antagonists (LAMAs). In asthma, the efficacy of LAMAs administered add-on to inhaled corticosteroids (ICSs) or ICS/LABA combinations has been investigated only in recent years. The aim of this systematic review was to examine the current literature concerning the impact of LAMAs on small airways and their lung deposition in both COPD and asthma. LAMAs administered either alone or in combination induced an effective bronchorelaxant effect of small airways, however the effectiveness of respiratory medications not only relies on the selected drug, but also on the employed inhalation device and patient's adherence. Tiotropium delivered via Respimat (R) SMI achieved a superior drug deposition in the peripheral lung compared to HandiHaler (R) dry powder inhaler and metered-dose inhalers (MDIs). The use of co-suspension (TM) delivery technology for MDIs and the introduction of the eFlow (R) nebulizer to deliver glycopyrronium improved aerosol drug delivery to the peripheral lung, by achieving uniform distribution of drug particles. This systematic review provides a synthesis of current literature concerning the impact of LAMAs on small airways and an insight on LAMAs distribution within the lung.