Among the areas covered by USP's new informational chapter are:

• Good Glass Supply-Chain Practices: The chapter recommends steps for manufacturers in selecting a glass container vendor, including auditing the supplier, obtaining glass formulation from the supplier, designating formulation of Type 1 glass (33 glass or 51 glass), determining tubing glass source(s), and determining whether the containers have been treated with ammonium sulfate, among others.
• Glass Surface Chemistry: This section discusses use of the aqueous chemistry of surface glass to decide on the potential drug product formulation and treatment steps that could increase glass stability.
• Factors that Influence Inner Surface Durability: This section offers information on factors that have the potential to influence the durability of the inner surface of glass containers. These factors include glass composition, the conditions under which the containers were formed, subsequent handling and treatments, and the drug product in the container. The section notes that not all factors influence surface durability to the same extent, and their effects can be additive.

The draft general chapter also details screening methods to evaluate inner surface durability. These build upon General Chapter <660>. At present, each lot of Type I glass containers received by a pharmaceutical manufacturer must comply with the Surface Glass Test detailed in General Chapter <660>. Although this test provides an indication of the durability of the surface, it does not provide a direct correlation with the susceptibility to form glass particles or to delaminate. The most important variable that affects surface durability is the drug product itself (i.e., the interaction between the product and the container). The Surface Glass Test does not take the drug product into consideration. Therefore, as USP states in the general chapter, this test represents only the first step in quality control of surface durability, and additional screening methods should be employed.

Predictive screening methods help evaluate glass containers from different vendors, glass formulations, and post-formation treatments. The general chapter addresses the three key parameters that screening methods should employ as well as commonly used analytical methods for evaluating the three parameters. It notes that predictive tests should look for precursors that lead to delamination rather than flakes themselves, and should be able to quickly provide predicative indication of surface durability. The general chapter also details other testing that may be useful, particularly in evaluating interaction with specific drug products.

Anthony DeStefano, PhD, is senior vice-president of compendial science, and Desmond Hunt, PhD, is senior scientific liaison, both with the US Pharmacopeial Convention (USP).