Definition: A filter needle is a needle with a small built-in filter, used to draw liquid into a syringe while holding back particles. Its best-known use is with glass ampules: snapping an ampule open can drop tiny glass fragments into the liquid, and the filter is meant to catch them.
A 2018 literature review in Annales Pharmaceutiques Françaises looked at 18 studies. Most found particles in liquid taken from glass ampules. Pooling seven studies, drawing the liquid through a filter needle cut the count of particles larger than 10 μm by 83%. The authors say the studies do not show what those particles do in people, so the best use of filter needles is still open.
A 2021 study of 56 nurses found glass particles in 449 of 672 ampoules opened. How the ampoule was wrapped and broken changed how many particles there were.
An ampule is a sealed glass container whose neck is snapped off to open it. A vial has a rubber stopper that a needle passes through, so it is not broken open. Most peptide vials people track are stoppered vials. Some vial systems have a filter built in instead: the Kovaltry vial adapter includes a 15 micrometer filter.
A filter is not a fix for a bad product. Liquid that looks cloudy or has visible bits is a reason to stop, not to filter. Pen labels such as Lantus and Xyosted say not to use a product that is cloudy or has particles. If you see that, note it on the vial in your log and set the vial aside.
Read more on Dose Track: Tracking vials and supplies · Using the reconstitution helper