Abstract
Because proteins and peptides are poorly absorbed through the gastrointestinal tract, the lungs are a promising organ for administering these substances because of their large inner surface area, thin epithelium, and relatively low protease activity. Pulmonary absorption rate constants are inversely related to molecular weights. Adding an absorption enhancer is a promising method to increase systemic bioavailability of inhaled peptides and proteins. The local lung toxicity of soluble powder seems to be minimal. Spray drying is a useful and widely applied technique to prepare powders for inhalation, and supercritical fluids have recently been used for producing such powders. Selecting operating conditions and adding proper additives such as sugars yields hollow porous particles, which are easily dispersed and avoid phagocytic clearance in the lungs, with maximized chemical and physical stability.
