Fundamentals of dry powder inhaler technology

Abstract

Dry powders and their delivery devices are an alternative to pressurized metered dose inhalers for the administration of aerosols to the lungs. Use of powders would reduce the necessity of employing global warming propellants; however further developments are needed in the technology required to disperse dry powders as aerosols if there is to be an alternative to pMDI as the primary means of aerosol delivery. For progress to occur the following factors influencing dry powder dispensing and dispersion must be considered. (1) The way in which particles are prepared may influence their subsequent behavioral characteristics. These preparative techniques fall in the general categories of constructive and destructive methods. (2) Specific morphological characteristics of particles such as size, shape, and rugosity may influence their interaction. In addition, particles may interact with each other or with surrounding surfaces. Among the underlying forces giving rise to these interactions are electrostatic, van der Waals, capillary and mechanical interlocking forces. (3) Powder may be dispersed by laboratory equipment, dry dust and fluidized bed generators, or small hand held devices designed for delivery of drugs to the lung. A development program requires selection of optimal conditions for each of these steps in the delivery of drugs to the lungs. The following description of dry-powder production, dispersion in air and particulate interactions discusses some of the difficulties that must be overcome for systems to advance as alternative to MDIs.