Question: how are inhaled drugs absorbed?
Answer: The most significant barrier to absorption of inhaled drugs is the epithelium of the lung (1). It is thick (50–60 μm) in the trachea, but diminishes in thickness to an extremely thin 0.2 μm in the alveoli. The change in cell types and morphology going from trachea, bronchi, and bronchioles to alveoli is very dramatic.