A Tolerance Interval Approach to Assessing the Biosimilarity of Follow-On Biologics

With many important biologic products due to lose patent protection in the next few years, the development of follow-on biologics has received much attention from both sponsors and regulatory authorities. Biologics are often produced in living systems. The living systems used to produce biologics are highly complex and could be sensitive to very minor changes in the manufacturing process. According to the guideline published by the European Medicines Agency, biosimilar products are similar, not identical, to the innovator products they seek to copy. Therefore, in developing a biosimilar, it is important to assess the similarity between it and the innovator product. In this article, we consider a two-arm, parallel design with a reference biological product and a biosimilar. Then, we construct a biosimilarity index for assessing the degree of similarity based on the tolerance limits. The acceptance criterion is proposed to judge whether the biosimilar is similar to the reference product. We also address the determination of the number of subjects to ensure that the occurring probability of biosimilarity criterion is maintained at a desired level, say 80% or 90%. Supplementary materials for this article are available online.