Excipient Compatibility and Functionality

Excipient selection is based on their functionality, compatibility, and variability of critical material attributes within an acceptable range for a given drug product. Drug-excipient compatibility studies are usually used as a screening tool to identify potential incompatibilities that alter physical, chemical, microbiological, or therapeutic properties of the drug in the dosage form. Excipient functionality involves the identification of critical material attributes based on target material properties and the functionality-related characteristics that impact the in-process and finished product quality attributes. Understanding the mechanistic basis of functional role and the commonly encountered range of variability of excipient attributes helps identify the acceptable range of excipient variability in a given drug product. This chapter describes contemporary practices in the identification of functionality-related characteristics of excipients; compatibility study designs and data interpretation; and understanding excipient variability and its impact on drug product quality attributes with examples and case studies.