Control strategy for subvisible particulates of therapeutic protein injections in pre-filled syringes using flow imaging

Pre-filled syringes (PFSs) are a widely used container closure for therapeutic protein injections, enabling simplified preparation and at-home administration. PFSs are commonly lubricated with sprayed-on silicone oil (SiO), which may migrate into drug product as SiO particles during storage and transportation. Elevated subvisible particle (SVP) counts from SiO present challenges for meeting USP 〈788〉 specification and may raise potential immunogenicity and toxicity risks. Light Obscuration (LO), the primary compendial method for PFS product release and stability testing, cannot differentiate SiO SVPs from proteinaceous SVPs. This drives the need for more comprehensive SVP characterization approaches for PFS products. Microflow Imaging (MFI) measures SVP count, size distributions, morphology and could differentiate fibrillar and translucent proteinaceous SVPs from spherical SiO SVPs using a morphological Aspect Ratio (AR) < 0.85 filter. This manuscript proposes a SVP control strategy for PFS products using MFI, supported by data demonstrating sensitivity to particle detection and stability-indicating capability. Additional data from orthogonal FlowCam (for counts) and complementary Raman Microscopy (for SiO identification) are presented. For Protein X, MFI was tested on multiple lots and shown as effective characterization tool to develop a product-specific control strategy. The proposed SVP control strategy holds considerable promise to assess and control SVP for injectable drug products.