Pharmaceutical excipients refer to excipients and additives used in drug production and formulation; they are substances that are not active pharmaceutical ingredients or prodrugs, have experienced appropriate safety evaluation, and are usually included in drug products.

Pharmaceutical excipients, a significant part of pharmaceutical preparations, are physical basis for ensuring the manufacture and use of preparations, and can determine the preparations’ performance, safety, efficacy, and stability.

Pharmaceutical excipients used in preparations usually have specific functions nd belong to different functional categories (General Chapter 0251). The physicochemical properties that have an important impact on the excipients’ functions and drug products’ performances can be called functionality-related characteristics (FRCs). For example, the particle size of a diluent may affect the formability of solid preparation; the molecular weight of thickener may affect the viscosity of liquid preparation. Thus, particle size and molecular weight belong to functional related indicators. The determination, classification, and limit range of functionality-related indexes are significant for ensuring the quality of preparations.

The Guidelines introduces the commonly-used and functionality-related indicators and research methods according to the functional categories of pharmaceutical excipients. The functionality of pharmaceutical excipients generally depends on their physicochemical properties. In some cases, they may also be affected by by-products or other additives in pharmaceutical excipients. Pharmaceutical excipients need to perform their functions in the preparation, whose formulation and technology may have a significant impact on the performances of the functions. Therefore, the evaluation of functionality-related indexes of pharmaceutical excipients should be aimed at specific preparations and their formulation technology, and a variety of research methods are usually used to study functionality-related indexes.

Pharmaceutical excipients can be characterized by various physicochemical properties. The functional indicators of pharmaceutical excipients mainly involve 19 categories of pharmaceutical excipients, such as diluents, that are difficult to evaluate their functionality by general chemical methods.

The Guidelines does not cover the functional indicators and evaluation methods for single component compounds or excipients (pH adjusting agents, osmotic pressure adjusting agents, bacteriostatic agent, flavoring agent, colorant, antioxidant, propellants, etc.) whose functionality can be evaluated by corresponding chemical methods. Hollow capsules will be addressed in other guidelines.

This Guidelines is not mandatory. Pharmaceutical excipient suppliers and users shall evaluate the functional indicators by themselves and clarify the research methods according to the characteristics of pharmaceutical excipients and the possible impact of excipients on the performance of preparations. Because the same pharmaceutical excipients may play multiple functions in the same preparation formulation, appropriate evaluation indexes, and research methods should be established for different functional categories. Researchers can also set up functional categories, functionality-related indicators and research methods that are not covered by this Guidelines at their discretion.