Fig. 3.

Influence of silicon oil on particle counts determined by a modified version of the USP Chapter 788 “Microscopic particle count test”. DS, drug substance; PFS, pre-filled syringes. Silicon oil droplets are not retained by the filter. Similar counts were obtained for the drug substance before and after storage in pre-filled syringes, as well as for the pre-filled syringes stored >6 years at 2–8°C (Aged MAb1 PFS). The increase in particle numbers observed by flow microscopy and light obscuration upon storage in pre-filled syringes can be attributed to silicon oil droplets and not to protein (or extraneous) particles