Silicone oil in protein drug products and its implications for formulation stability

High-concentration biologics are transforming patient care by making potent injectable therapies easier and more accessible. But these biologics come with real stability hurdles. Proteins at these concentrations are more prone to clumping, misfolding, and aggregation that can undermine the drug product's safety and effectiveness. Silicone oil, a common syringe lubricant, helps ensure smooth injections but often leaches and migrates into the drug solution. Hydrophobic protein regions adsorb at oil-water interfaces, nucleating smaller aggregates that propagate into larger ones under agitation. Continued exposure to leached silicone oil during storage/ transport can accelerate the generation of protein particles. These particles have the potential to increase immunogenicity in patients, making this a significant risk from both clinical and regulatory perspectives. To combat these issues, innovative solutions such as advanced coatings, protective surfactants, optimized buffer systems, and silicone oil-free syringes are being explored, alongside device engineering and gentler process controls. Together, smarter formulation choices, device breakthroughs, and streamlined processing will pave the way for safer, more stable high-concentration biologics in next-generation syringe systems. This review provides a brief overview of silicone oil characteristics and its interactions with proteins, and discusses possible solutions to minimize silicone oil-induced protein aggregation.