Recent advances in controlled pulmonary drug delivery.

Characterized by large surface area, high vascularization and thin blood-alveolar barrier, drug delivery by the pulmonary route has benefits over other administration routes. However, to date most of the marketed inhalable products are short-acting formulations that require the patient to inhale several times every day, thus reducing patient compliance. Controlled pulmonary drug delivery is a promising system but the formidable airway clearance mechanisms need to be avoided. This review mainly introduces the barriers impeding the development of controlled pulmonary drug delivery and strategies used to overcome them. We believe that large porous particles, swellable microparticles and porous nanoparticle-aggregate-based particles are the most promising carriers to control drug release in the lung.