A retrospective study presented by Rahul Khurana, MD, at ASRS 2017 in Boston provides additional evidence that injections of bevacizumab may introduce silicone oil droplets into the vitreous cavity.
Using dilated biomicroscopy, Dr. Khurana and his colleagues identified 60 cases of silicone oil droplets among patients treated at their retina practice over a 14-month period. During this time span, the practice administered a total of 6,632 bevacizumab injections, most of which were given through single-use 31-gauge BD insulin syringes (Becton, Dickinson and Company) prepared by a 503B-approved compounding pharmacy (California Compounding Pharmacy, Newark, CA).
Overall, 32% of cases were asymptomatic and 68% reported spots of light and floaters that resolved without intervention within 2 to 8 months. There was no evidence of inflammation, IOP increase or corneal edema in these patients, and none required vitrectomy.
Of note, there was only 1 documented case between October 2015 to April 2016 (0.03%). Between May to November 2016, however, the number of cases jumped to 59 (1.7%). But why the sudden increase in the prevalence of silicone oil droplets? Dr. Khurana hypothesized that a change in the manufacturing process of the insulin syringes could be the underlying reason.
Additionally, Dr. Khurana noted that not priming the syringe before injection was associated with a 15-fold higher risk of droplets compared with priming (P<0.001).
In a separate presentation, Geoffrey Emerson, MD, PhD, substantiated this theory with findings from an experimental study that evaluated silicone oil expulsion by different syringe types. After loading a variety of syringes with fluorescein dye and injecting the contents onto glass slides, Dr. Emerson noted that only the BD insulin syringes expelled silicone oil alongside the dye. Additionally, the silicone oil contained in these syringes as a lubricant was only emitted at the end of the injection, when the plunger was maximally advanced.
Both Drs. Khurana and Emerson advocate using Luer-cone design syringes do not contain silicone oil.
To conclude his talk, Dr. Khurana emphasized that physicians should prime their syringes prior to injection and counsel their patients on the risk of floaters associated with preloaded insulin syringes.