Assessing the bioequivalence of biosimilars The Retacrit case.

This first phase of the first generation of modern biotechnology-derived protein drugs is now coming to an end with the expiration of their patents and consequently the possibility of the marketing of copies. The generic paradigm used for classical drugs cannot, however, be applied to therapeutic proteins because of their complexity. The European regulatory system issued its first comprehensive guidelines for the development of the so-called biosimilars. A number of these products have now been introduced to the European market. The case of Retacrit, one of the biosimilar epoetines, is being discussed as an example of the challenges encountered when assessing the bioequivalence of therapeutic proteins.