Quantitative Evaluation of Insoluble Particulate Matters in Therapeutic Protein Injections Using Light Obscuration and Flow Imaging Methods

Flow imaging (FI) has emerged as a powerful tool to evaluate insoluble particles derived from protein aggregates as an orthogonal method to light obscuration (LO). However, few reports directly compare the FI and LO method in the size and number of protein particles in commercially available therapeutic protein injections. In this study, we measured the number of insoluble particles in several therapeutic protein injections using both FI and LO, and characterized these particles to compare the analytical performance of the methods. The particle counts measured using FI were much higher than those measured using LO, and the difference depended on the products or features of particles. Some products contained a large number of transparent and elongated particles, which could escape detection using LO. Our results also suggested that the LO method underestimates the size and number of silicone oil droplets in prefilled syringe products compared to the FI method. The count of particles ≥10 μm in size in one product measured using FI exceeded the criteria (6000 counts per container) defined in the compendial particulate matter test using the LO method. Thus precaution should be taken when setting the acceptance criteria of specification tests using the FI method.