Dye Ingress, a Poor Bet in a High Stakes Game
The dye ingress test method continues to be a widely used test method for Container Closure Integrity (CCI) within the pharmaceutical industry. For high risk parenteral applications this method is not a suitable approach due to reliability of the method and measure. For applications with large molecule drugs or for prefilled injectable container formats, the use of a dye ingress test method will simply not work. There is an active campaign to understand all the dynamics and implications of deploying a CCI test method. The transition to a deterministic test method for high risk CCI applications is a matter of common-sense patient safety.
The August 2016 revision of the United States Pharmacopeia (USP) chapter 1207 “Package Integrity Evaluation—Sterile Products,” lays out a blueprint for more deterministic test methods. The document drives a clear agenda, encouraging validation of factors facing any test method. While USP 1207 does not outright reject the use of the dye ingress method, the basic framework would exclude its use for many applications.
USP 1207 is not groundbreaking in terms of the prescribed approach to quality control, it simply clarifies that traditionally used test methods may have significant limitations.
New concepts such as the Maximum Allowable Leakage Limit (MALL) shift conventional thinking related to CCI. All containers leak to some degree. Understanding what level of leak, whether through prior research or through investigation, provides the requirements for patient safety. That requirement can then be used to identify the appropriate test method. For parenteral product classes, defects in the single micrometer range are considered critical.
To date the chief criticism of the dye ingress test method has been subjectivity of the visual inspection stage of the test. With today’s proliferation of large molecule treatments, the case against the dye ingress method must be reestablished. There is a greater limitation to the dye ingress method associated with the actual physics of the test.
The Dye Ingress
There is no global standard for the dye ingress test method, and it is important to note that different international regulatory bodies differ on their prescribed approach. The dye ingress method is similar to the water bath but requires a series of events to occur for a defect to be effectively detected. The method begins with (1) submerging the container beneath a dye solution inside a vacuum vessel and drawing vacuum on the vessel. (2) Under the vacuum a defective sample would need to leak contents into the dye solution. (3) Upon bringing the vessel back to atmospheric pressure the vacuum developed inside the container in stage (2) would draw dye back into the container.
The primary probabilistic challenges facing dye ingress are associated with stage (2) of the test cycle:
- Enough volume needs to be evacuated from the container during stage (2) of the cycle to create enough vacuum inside the container to draw the dye into the container.
- If there is little to no air inside the container, little to no force will be generated in stage (2) to draw liquid from the container. In this circumstance, dye ingress in stage (3) is highly probabilistic.
- If there is air in the container, the chemical properties of the container contents will determine how effectively fluid contents can leak out of the container during stage (2). The vacuum applied in stage (2) will be less effective at drawing liquid from the container, especially with more viscous liquids.
The basic list of factors that will impact a dye ingress leak test method include the dye bath surface tension, test method pressure levels, container headspace and product chemistry. The FDA and EMA require CCI testing to be performed with actual product or product mimicking the natural product physical and chemical conditions. Generally, there is little standardization for the dye ingress test, and the impact of container and product conditions on the method’s performance further impedes the method’s capability.  Large molecule products will greatly impede product leakage during the test method, which prevents dye from penetrating a defect in the final stage of the test.
Recent research has attempted to support the use of dye ingress. The study deployed the use of microcapillaries as the defect for its positive controls. Regardless of the internal diameter of the microcapillaries, the study fails to fully recognize or eliminate the false implications created by using microcapillaries. Fundamentally capillaries do not interact with blue dye or product the way a normal critical defect does.
The use of capillaries and micropipettes are at the effect of liquid surface tension and associated physics of the capillary volume. All research that has defended the use of the dye ingress test method has only used capillaries as a defect or a vial with headspace volume as the container of choice to produce favorable results. All research that has identified the dye ingress as probabilistic and ineffective have either used leaks in the glass body of the container or have used prefilled injectable devices with little-to-no headspace.
The Path Forward
There are many alternatives to the dye ingress method. USP 1207 did not only create an extensive list of current effective deterministic methods, it also describes each method in detail stopping short of describing exactly how to execute the method. Current scientific research has defined appropriate norms for effective container closure integrity testing. Broad and indiscriminate application of any method without thorough validation will lead to critical failures. Recognizing when a method is appropriate and effective in establishing container closure integrity is vital to any organization’s success. Distinct choices made in pursuing patient safety have lasting effects on an organization.
- United States Pharmacopeia. USP Regulatory Guidance Document: Chapter 1207 Package Integrity Evaluation—Sterile Products
- Kirsch, Lee E., Lida Nguyen, Craig S. Moeckly, and Ronald Gerth. “Pharmaceutical Container/Closure Integrity. II: The Relationship Between Microbial Ingress and Helium Leak Rates in Rubber-Stoppered Glass Vials.” PDA Journal of Pharmaceutical Science and Technology 51, no. 5 (September–October 1997): 195–202.
- Victor, Ken G., Lauren Levac, Michael Timmins, and James Veale. “Method Development for Container Closure Integrity Evaluation via Headspace Gas Ingress by Using Frequency Modulation Spectroscopy.” Journal of Pharmaceutical Science and Technology 71, no. 6 (November–December 2017): 429–53. doi:10.5731/pdajpst.2017.007518
- Wolf, Heinz, Tony Stauffer, Shu-Chen Y Chen, Yoojin Lee, Ronald Forster, Miron Ludzinski, Madhav Kamat, Brian Mulhall, and Dana Morton Guazzo. “Vacuum Decay Container/Closure Integrity Testing Technology. Part 2. Comparison to Dye Ingress Tests.” Journal of Pharmaceutical Science and Technology 63, no. 5 (September–October 2009): 489–98.
- Handbook, Nondestructive Testing. Leak Testing. 3rd ed., vol. 1. Columbus, OH: American Society for Nondestructive Testing, 1998.