**6.3 Microparticles**

The human lung is equipped with mechanisms to remove deposited particles by mucociliary clearance and phagocytosis. These clearance mechanisms should be considered while designing protein or peptide therapeutics and nanoparticles as a vehicle. The aim should be to achieve more efficient absorption and sustained therapeutic effect. It has been reported that inhalation of large porous insulin particles resulted in an elevated systemic level of insulin [165]. On the other hand, small non-porous insulin particles did not sustain therapeutic effect (4 hours vs. 96 hours for large porous particles). It has also been reported that the pulmonary delivery of insulin with nebulized DL-lactic/glycolide copolymer nanoparticle resulted in more sustained release (48 hours vs. 6 hours) compared to the nebulized aqueous solution [166].
