Researchers have found that, in rare cases, zinc from the needle shield can leach into the drug solution to be injected and possibly contribute to syringe clogging. They were asked by the pharmaceutical company MSD (a trade name of Merck & Co., Inc., Rahway, NJ, USA) to find out whether tiny amounts of the element zinc can get inside the needles of pre-filled syringes and, if so, where it lodges in the needles.
The background is the observation that, in rare cases, the needles of pre-filled syringes (PFS) can become blocked, for example if the syringes are not stored in a cool enough environment. This phenomenon has been known for some time. However, what has remained unclear is exactly what triggers the blockage. One suggestion was that zinc from the needle shield — the rubber cap into which the needle is inserted when the syringe is manufactured — could leach into the drug solution to be injected, making it more viscous, which would ultimately lead to blockages.
This meant that several questions had to be answered. Is there zinc inside the needle? And if so, where do they come from? What does the inside of a clogged needle look like? And is the zinc also present in the solution being injected, which could ultimately lead to the blockage?
MSD was able to answer the first question in-house using mass spectroscopy. Yes, the dried solution in the needle contained zinc, and this had to come from the needle shield. This followed from the fact that no zinc was detected in a control experiment in which the needle shield was omitted. However, to carry out these analyses MSD first had to extract the material from the needle and then feed it into the mass spectrometer. This meant that the MSD researchers could not determine exactly where the zinc was located in the blockage. To answer this, they needed analytical methods that went beyond the scope of a conventional laboratory. They found these at ANAXAM.
As a technology transfer center, ANAXAM offers its customers unique imaging and spectroscopic methods that can be achieved using the large research facilities at PSI.
SLS’s TOMCAT beamline can be used to produce computed tomograms. The system works much like a CT scan in a hospital, but uses synchrotron radiation, special X-rays which are partially coherent and can therefore interfere with each other. This property allows researchers to visually record even the tiniest amounts of material in an ultra-thin hypodermic needle made of stainless steel – with an internal diameter of less than 200 µm. In this particular case, the result was a clear image of the dried solution inside the clogged needle.
