Dry Powder Inhalers - An Overview

The drug product encompasses the pharmacologic activity with the pharmaceutical properties. The ideal characte-ristics are physical and chemical stability, ease of processing, accurate and reproducible delivery to the target or-gans and availability at the site of action. A Dry powder inhaler (DPI) is a device that delivers medication to the lungs in the form of a dry powder. For the DPI, these goals can be met with a suitable powder formulation, an efficient metering system and a perfectly selected device. This review focuses on the dry powder inhaler formulation, evaluation, material methods and development processes. Most of the dry powder inhaler formulation en-compasses micronized drug particles blended with larger carrier particles that promote the flow properties, re-duce aggregation and help in dispersion. A combination of the physicochemical properties, particle size, shape, surface area and morphology affects the forces of interaction and aerodynamic properties, which in turn deter-mine the fluidization, dispersion, delivery to the lungs and deposition in the peripheral airways. However the properties of free micronized powders often interfere with the drug handling and with drug delivery, reducing the dose consistency. Dry powder inhalers are evaluated by the drug product characterization studies such as the in vitro dose proportionality, effect of patient dose, priming etc. The development of the new designs of the DPI is governed by the driving forces such as the regulatory and pharmacopoeial requirements, delivery systems for the NCE, clinical factors and commercial factors.