Simon Cote

Simon Cote

Principal SME, Seals

December 30, 2013

Plunger Machinability: Steam vs Gamma

The two most common means of sterilizing elastomeric parenteral packaging components are steam autoclave and gamma irradiation processes. When appropriately validated, both processes are very effective at eliminating concerns around microbial contamination of the components used for container closure of sterile liquid, lyophilized or powder drug products. Despite the ability of both methods to reach the required sterilization specifications and requirements, the overall impact that these processes have on the elastomeric component can be quite different.

West has put considerable effort into understanding the multiple ways elastomeric components can be impacted by these sterilization processes. The two major areas of focus have been on drug product compatibility and filling line machinability. Per the studies conducted at West, steam sterilized elastomeric components had more desirable results both in terms of the extractable profile and the performance of the components on the filling line.

A machinability study was performed using one of West’s 1mL long syringe plunger designs. The study was composed of six sample sets of the same 1mL long plunger design, but of two different elastomeric formulations (4023/50 Gray and 4432/50 Gray) and three different methods of sterilization (steam autoclave processing, 10-20 kGy gamma irradiation and 40-50 kGy gamma irradiation). The goal of this study was to evaluate each sample set in the feeder bowl and tracks at various filling line speeds from 200 units/minute to 600 units/minute, and determine if the machining performance requirements were met.

The study results showed that the performance of the steam sterilized plungers was equal or better at the various filling line speeds than the plungers gamma irradiated to 10-20 kGy. The results from the study also showed that plungers gamma irradiated to 40-50 kGy performed considerably worse than the other two sterilization methods, and could not meet the machining requirements at the middle and higher range filling line speeds.

While many other elastomeric manufacturers of prefilled syringe plungers will gamma irradiate components to levels approaching 40 kGy, which is very close to the maximum a halobutyl rubber can withstand, West recommends the use of steam sterilization for elastomeric components. Upon customer request West will gamma sterilize elastomeric components at levels of 10-20 kGy.

For any questions and inquiries regarding the compatibility and machinability studies comparing steam to gamma sterilization processes please email or

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