Development of dry powder inhalers.

Development of dry powder inhalers involves powder recrystallization, formulation, dispersion, delivery, and deposition of the therapeutic agent in different regions of the airways in prophylaxis/ treatment/ diagnosis of pulmonary and systemic disorders. Conventional powder production by crystallization and milling has many limitations resulting into development of alternative techniques to overcome the problems. In the last decade many patents have been filed claiming improvement in aerosol performance of dry powder inhalers through the use of (i) incorporation of fines of carrier particles to occupy active sites on the surface and use of hydrophobic carriers to facilitate deaggregation through reduced surface energy and particle interaction (ii) reducing aerodynamic diameters through particle engineering and incorporating drug into porous or low particle density, and/or (iii) preparing less cohesive and adhesive particles through corrugated surfaces, low bulk density, reduced surface energy and particle interaction and hydrophobic additives. Moisture within dry powder inhaler (DPI) products has also been shown to influence aerosol performance via capillary force and electrostatic interaction. Better understanding of particle forces and surface energy has been achieved by the use of sophisticated analytical techniques. Understanding the intricacies of particle shape and surface properties influencing specific lung deposition has been further facilitated by the availability of newer and advanced softwares. A critical review of recent patents claiming different approaches to improve lung deposition of dry powder inhalers will help in deciding the focus of the research in the area of technological gaps.