By Christina Mendat, PhD
This is the fourth in a six-part series on prefilled syringes where we address some issues we’ve encountered in our multiple client engagements.
An increasing number of prefilled syringes are being developed with a sharps protection feature. An example is depicted in the figure below. The prefilled syringe is placed into an exterior housing that retracts once the injection has completed. The needle is retracted into the housing and the exterior housing locks into place around the needle. This is a wonderful feature and it is easy to understand its appeal. It provides protection from needle sticks and adds another level of protection once in the sharps container.
There are human factors issues that should be considered with these products, however. They include:
- Barrel spinning. With some variations on this design, the syringe barrel can spin within the exterior housing. This can make a few things difficult including a) viewing the syringe graduations, b) setting the orientation of the needle bevel, and c) orienting the flange position while viewing the syringe.
- Viewing the Syringe. Oftentimes, laypeople are not aware that they can spin the barrel. They assume the syringe is positioned where it is supposed to be, even if it is difficult to see the information.
- Low Dose Volumes. Setting low dose volumes in devices like these can be extremely difficult (and not just for laypeople, but for health care professionals as well). The exterior housing has a cutout that permits users to see through to the syringe barrel. The cutout seldom runs the whole length of the syringe barrel for obvious reasons, and the housing can still obscure some of the syringe barrel. Moreover, the spring can also make it hard to see the barrel and plunger. For medications with very low volume to administer, the housing and spring can make it difficult to see the liquid and can negatively affect a user’s ability to measure a dose accurately.