Interchangeability among reference insulin analogues and their biosimilars: regulatory framework, study design and clinical implications

Biosimilars are regulated differently from small-molecule generic, chemically derived medicines. The complexity of biological products means that small changes in manufacturing or formulation may result in changes in efficacy and safety of the final product. In the face of this complexity, the regulatory landscape for biosimilars continues to evolve, and global harmonization regarding requirements is currently lacking. It is essential that clinicians and patients are reassured that biosimilars are equally safe and effective as their reference product, and this is particularly important when interchangeability, defined as 'changing one medicine for another one which is expected to achieve the same clinical effect in a given clinical setting in any one patient', is considered. Although the automatic substitution (i.e. substitution without input from the prescribing healthcare provider) of biosimilars for reference products is currently not permitted by the majority of countries, this may change in the future. In order to demonstrate interchangeability between reference products and a biosimilar, more stringent and specific studies of the safety and efficacy of biosimilars are likely to be needed; however, guidance on the design of and the need for any such studies is currently limited. The present article provides an overview of the current regulatory framework around the demonstration of interchangeability with biosimilars, with a specific focus on biosimilar insulin analogues, and details experiences with other biosimilar products. In addition, designs for studies to evaluate interchangeability with a biosimilar insulin analogue product are proposed and a discussion about the implications of interchangeability in clinical practice is included.