Factors affecting defining the quality and functionality of excipients used in the manufacture of dry powder inhaler products

The successful manufacture of a regulatory approved dry powder inhaler (DPI) product is only achievable by applying robust control systems to all aspects of analytical, engineering, and material based processes. Whilst many aspects of DPI drug product manufacturing can be adequately controlled, it is often the control of materials, that is, drug substance and excipients, which can lead to variation in the quality of the final drug product. This article gives an overview of DPI excipients and highlights the challenges of defining and, importantly, understanding the relationships between quality and functionality for excipient components in DPI formulations.