Pulmonary Delivery as a Route for Insulin

The pulmonary route of administration offers several advantages. First, the lung has a large surface area for drug absorption, ranging from 100 to 140 m2. In addition, the alveolar epithelium has permeability that allows for rapid absorption of solutes. Because the mucociliary clearance of the alveolar lung tissue is slower than that of the bronchiolar tissues, the alveoli provide a greater opportunity for the absorption of larger molecules (e.g., insulin). Studies have shown that particle size should be between 1 and 3 micrometers in diameter for optimal deposition in the lung, and that dry powder formulation can deliver more active drug in a single inhalation than liquid aerosol formulations. Patient-controlled variables (e.g., inhalation flow rate, inhaled volume, and duration of inhalation) also need to be controlled for optimal deep-lung insulin delivery. The pharmacodynamic effects of insulin formulations administered via the lung are comparable to, or even faster than, those of subcutaneous injected regular insulin or rapid-acting insulin analogues.