With the advent of more unique package systems and the development of biological products, the use of a syringe as a standalone package system has become much more widespread. While most syringes are constructed of glass (we will discuss plastic syringes in a future article), and the glass used is typically a type one borosilicate, the United States Pharmacopeia is clearly defined in referencing relevant qualification procedures under general chapter 660. The test procedures outline all the basic requirements that will enable the glass syringe to be used for a pharmaceutical grade product.
For many companies, the basic USP 660 qualification may not be enough. In many instances, the syringes are designed to hold a small volume ( 1 ml of drug product). Construction of such small components can lead to even slight syringe to syringe variation in areas like key dimensions that may have a negative effect on the administration of the product. As a result, and to prevent end user complaints, many companies using syringes on a routine basis are performing more extensive qualification testing. The development of a qualification test plan for a glass syringe should encompass three key areas: USP or EP qualification of the Glass Material, Dimensional Analysis of the Syringes on a lot to lot basis and functional testing to insure effective use for the end user.
The routine qualification under a prescribed test method like the USP or EP should be the basic first step. There is no value in performing dimensional or functional testing on a glass materials that does not meet the basic standards already established.
The second step in the qualification plan should focus on dimensional analysis. Working from an engineering specification sheet (that should be required documentation with each lot of syringes), a set of key measurements points can be established and the acceptable tolerances will be documented on the drawing. The tools for analysis typically include an optical comparator, a video microscope and smaller measurement tools like calipers. It is critical to insure that any and all instruments used be calibrated to NIST traceable standards. The actual number of samples to be tested can vary from a handful to many hundreds per lot. Some quality people may require that a sample set based upon the military spec sheet for sampling be followed. In this case, the actual number of samples to be tested would be based on the overall size of the lot. For ease of use, it is suggested that a sample size of 50 units be tested as this will provide, in most cases, a good representative sample and provide enough data points to be of statistical significance.
The final step in the three part qualification process centers on functional testing. One key functional test that has grown in use over the past several years is syringe barrel strength. This test evaluates the overall glass strength by using an Instron instrument to break or crush the syringe barrel. The Instron instrument is generically known as a universal testing machine and is designed to evaluate the mechanical properties of products and components. Using the Instron technology items such as tension, compression, flexure, fatigue, impact, torsion and hardness can be effectively evaluated. With regard to syringe testing the tension and compression functions are best utilized and this provides great insight into the overall quality of the glass. In addition, there are a number of other tests that can be performed to insure the syringe, and the other components used in conjunction with it, work in an effective manner. Again, sing the push/pull technology of an Instron, items like needle pull off force, syringe plunger glide ability, and needle shield removal can be evaluated. These are all critical items that can affect the end user – and lead to complaints and malfunctions.
As your company moves to the use of glass syringes, take a moment to evaluate the qualification options available and work to outline a plan that helps you meet regulatory requirements while preventing end use functional failures (and complaints).