From bioequivalence to biosimilars: How much do regulators dare?

The main advantage of an abbreviated licensing pathway is the possibility of extrapolating efficacy and safety data from an original medicinal product to a subsequent "copy" version, thereby reducing the clinical development programme in particular. For small-molecule chemically synthesized generics, such an abbreviated licensing pathway was established decades ago, whereas it was only more recently implemented for similar biological medicinal products, so-called biosimilars. Clinicians and patients have repeatedly expressed concerns about the efficacy and safety of biosimilars, especially in 'extrapolated' indications for which no own clinical data have been generated. Generic drugs usually contain well-defined active ingredients whose "identity" with that of the originator, the so-called reference product, is easily verifiable. Biological substances are generally more complex and difficult to characterize. They are produced in living organisms and therefore naturally exhibit some intrinsic variability, i.e. microheterogeneity. Since the chosen expression system and the manufacturing conditions influence the quality characteristics of a biological substance, mostly its posttranslational modifications such as the glycosylation pattern, it is unlikely that two independent manufacturing processes can achieve completely identical biologicals. A biosimilar, especially if it is a glycoprotein, can therefore, at best, be highly similar to the reference product. It seems that the not-identical-but-(highly)-similar-paradigm for biosimilars is often not well understood and causes confusion. However, while at first glance an abridged approval pathway for biosimilars appears to be daring, it is in fact based on sound scientific reasoning. A biosimilar applicant has to provide a considerably larger package of comparative data than a generic applicant to ensure that the biosimilar can indeed rely, for the purpose of licensing, on the efficacy and safety experience gained with the reference product. While for a generic, the demonstration of similar in vitro dissolution and in vivo bioavailability (so-called 'bioequivalence') is sufficient to conclude therapeutic equivalence with the reference product, for a biosimilar, comparable physicochemical, biological and functional characteristics as well as efficacy and safety/immunogenicity with the reference product must be demonstrated. In addition, unlike generics, any extrapolation to other indications of the reference product must be scientifically justified. More than 10 years of successful clinical experience with biosimilars in the EU support the credibility of the scientific principles guiding the biosimilar concept. So far, there has been no need for either withdrawal of an approved biosimilar or for additional labelling because of efficacy or safety concerns.