Avastin eye injections are an off-label (not FDA approved) use of this drug for the treatment of macular degeneration, retinal vein occlusion, diabetic macular edema, and diabetic retinopathy. Compounding pharmacies which are usually state-licensed operations buy the Avastin from distributors and then prefill an empty syringe with the drug. This prefilled syringe is then sent to your eye doctor. Many such compounding pharmacies use syringes that are not designed for injection into the eye. It is these syringes that are the source of the silicone, because they are lubricated in several places with silicone oil.
In addition to lubrication of the needle itself, both the barrel and plunger of the syringe are coated with silicone oil. One of the undesirable properties of silicone is that it tends to migrate and therefore can be displaced from the surface to which it is originally applied. When a silicone-coated syringe in prefilled with Avastin, the silicone oil is directly exposed to and mixes with this liquid drug in the barrel of the syringe. If there is a period of several weeks between the time of the filling of the syringe and the eye injection, this allows more time for the silicone to migrate into the Avastin. And at the time of the eye injection when the plunger squeezes against the inside surface of the syringe barrel, there is another opportunity for more silicone to be injected into the eye along with the Avastin.
There are better and safer syringe technologies for use with eye injections and which would prevent silicone particle contamination of the eye with Avastin treatment. We will discuss those in upcoming entries on this blog.