The Plunger Blues

by Christina Mendat, PhD

This is the third in a six-part series on prefilled syringes where we address some issues we’ve encountered in our multiple client engagements.

What’s in a plunger you may ask? A lot more than one may think. A plunger is a plunger right? So, how do you set the dose? Some plungers have a more conical shape whereas others have a flat shape. For laypeople, and even health care professionals, the conical plunger can be quite confusing. Example, what is a conical base? You’d be surprised how many interpretations we’ve heard.

plungers

Although prefilled syringes come “prefilled” there are times that variable doses are required. Some of these dose volumes can be extremely low (e.g., .25 – .45mL). To that end, the graduations, label, and plunger-type become extremely critical. Will users be able to find the appropriate setting and if not, how can this be addressed?

In a recent study using a conical shaped plunger, a number of experienced healthcare professionals (physicians and registered nurses) struggled with determining when they had set the dose correctly. Specifically, there was confusion as to how the dose should be read (i.e., at the top of the conical shape or the bottom of the conical shape). There was no consensus on how the dose should be read using the conical shaped plunger. Had a flat shaped plunger been employed, this confusion would likely have been prevented.

If your drug has limited +/- variability, as it relates to drug volume, it may be wise to think hard about the plunger that has been selected and how it will interact with other device features. Most importantly, will users be able to set the intended dose?