A simple method for the detection of insoluble aggregates in protein formulations

Low levels of insoluble aggregates in protein formulations can sometimes only be detected by visual inspection. To overcome the subjectivity and other limitations associated with visual inspection, a microscopic technique based on filtration/staining was developed. This method is a simple modification of the microscopic method listed in USP for particulate matter analysis and it provides two major advantages over the original method. First, particles are easier to see because of the staining. Second, this method is specific to protein aggregates so that it avoids interferences from other nonproteinaceous particles. In addition, this method does not have any restrictions on the rheological or optical properties of the samples. This method can be a useful tool in protein formulation development as demonstrated by its application in the evaluation of monoclonal antibody formulations.