INTRODUCTION

The purpose of this chapter is to explain how excipients may be used in formulations and how they relate to compendial specifications, performance-related properties (PRPs), critical material attributes (CMAs), critical quality attributes (CQAs) of the drug product, and quality by design (QbD) principles that aid in their selection and control. Excipients are used in virtually all drug products and are essential for drug product manufacturing and performance. To ensure robust drug products with consistent quality, the excipients must be appropriately specified. Excipients used in drug products typically are manufactured and supplied in compliance with compendial standards. However, the impact of excipient properties on the quality and performance of a drug product may be unique for each formulation and process and could depend on properties of excipients that are not evaluated in USP or NF monographs and which may vary from supplier to supplier and batch to batch (see General Notices, 4.10 Monographs). The impact of excipient properties and their variability depends on the role of an excipient in a formulation and the CQAs of the drug product. A CQA is a physical, chemical, biological, or microbiological property or characteristic of the drug product that should be within an appropriate limit, range, or distribution to ensure the desired product quality (The International Council for Harmonisation (ICH) Harmonised Tripartite Guideline, Pharmaceutical Development Q8(R2), Step 4 version, August 2009).