Biological agents and biosimilars: Essential information for the internist

•Biologics are a wide range of substances synthesized by cells or living organisms.•A biosimilar is a copy of an authorized original biological medicinal product.•Safety and efficacy of biosimilars are comparable to the originator's.•The post-marketing safety evaluation is stringent as for any new biological product.

Biologics embrace a wide range of substances synthesized by cells or living organisms by means of different biological processes, including recombinant DNA technology, controlled gene expression, or antibody technologies. A biosimilar establishes similarity to the reference medicinal product in terms of quality characteristics, biological activity, safety, and efficacy based on a comprehensive comparability exercise. Minimizing development costs and accelerating their market access create a convergence of interests between health services, worried about sustainability, and generic manufacturers. While the demonstration of bioequivalence is sufficient for small synthetic molecules, this approach is not scientifically applicable to a copy of biological drug constituted by large and complex molecules, which are similar but not identical to the originator and are also subject to different post-translational processes. Internists should be confident that the development process of biosimilars ensures a comparable risk-to-benefit balance with the originators. On the basis of available evidence and pharmacovigilance network, there are no grounds to believe that the use of a biosimilar carries more risks for the patient than the use of an originator. Since the first biosimilar was authorized in Europe in 2006, no clinical alerts have raised red flags about the established EMA biosimilar pathway. In this article, we discuss some of the most frequent concerns raised by clinicians about biosimilars and try to explains the scientific principles underlying the biosimilar concept established in the EU in order to license biosimilar drugs.