While asthma Inflammation involves both the large and small airways, small airways are the major site of airflow limitation in asthma sufferers and therefore smaller drug particles are required in order to be effective in treating the smaller airways.
The small airways, also known as the “silent zone” and defined as those of less than 2mm in diameter, account for nearly 99% of the lung volume, and play an important role in the development of asthma. Inflammation and abnormalities in the small airways are associated with nocturnal asthma, exercise-induced asthma, allergic asthma, fatal asthma, severe asthma and mild asthma.
However, according to Dr Omar Usmani, reader in respiratory medicine and consultant physician: Imperial College London & Royal Brompton Hospital, drug particles contained in current inhalers predominantly target the large airways as the particles are too large to be deposited into the small airways.
He adds that improved drug formulations and enhancing the design of inhalers could play a significant role in achieving deposition in the small airways. “By not directing our inhaler therapies to treat the small airways we may not be fully treating all the inflammation throughout the airways - both large and small.”
Dr Usmani continues that drug particle size influences where and how much of the particle will be deposited and is therefore important in targeting both large and small airways. “Clinical and scientific studies have shown that smaller particles deposit in the more peripheral and smaller airways as well as the large airways, providing an improved total lung dose and reducing inflammation.”
With an estimated 33m people globally suffering from asthma, this condition is one of the world’s major non-communicable diseases and the most common non-communicable disease amongst children.
