Biosimilars in chronic inflammatory diseases: facts and remaining questions 5 years after their introduction in Europe.

Five years after the launch of the first infliximab biosimilar, biologics have found their place in the treatment of chronic inflammatory conditions, but there are remaining questions. This is a review of the introduction of antibody biosimilars in Europe; the reasons for their success and how biosimilar hesitancy was quailed. We provide an overview of the concepts of biosimilarity, extrapolation, and interchangeability, using examples in rheumatology and gastroenterology for illustration. A review of the evidence collected from switching studies using robust designs is included. Remaining questions such as 'inter-switching' are also discussed. Biosimilars have democratized access to powerful medicines. Efficacy and safety studies provided reassuring data, but knowledge gaps persist. The availability of so-called 'bio-betters' might open new avenues and change clinical practice.