Biosimilars: not original, not identical

Biosimilars have an identical amino acid sequence to their original reference product, although, unlike generic versions of small molecule medicines, they are not necessarily structurally identical or clinically interchangeable.1-3 Biosimilars are usually biotechnology-derived, complex mixtures of isoforms of a desired biological substance.1 The biological interactions of a biosimilar may be different from its reference product, which can translate to differences in clinical behaviour.1-3