Biosimilars Glossary

Biosimilars Education: Glossary

  • Biologic
    A substance derived from a living organism or its products that is used in the diagnosis, prevention or treatment of disease. Examples of biologic medicines include recombinant proteins, allergy shots, vaccines and hematopoietic growth factors.1,2
  • Biosimilar
    A biological product that is highly similar to an approved reference biological product notwithstanding minor differences in clinically inactive components, and for which there are no clinically meaningful differences between the biological product and the reference product in terms of the safety, purity and potency of the product.3
  • Critical quality attribute (CQA)
    A physical, chemical or biological property that must be within an appropriate limit, range or distribution to ensure the desired safety, efficacy and pharmacokinetics of a drug.4
  • Extrapolation
    The process by which a proposed biosimilar product may be approved for one or more additional conditions of use for which the reference product is approved but in which the biosimilar was not studied. Approval for use in these reference product indications may be granted if an appropriate scientific justification is provided and the totality of evidence addresses any identified differences between the biosimilar and reference product.3
  • Interchangeability
    Or an interchangeable product, in the US, is an FDA-designation that refers to a biosimilar that has undergone additional studies to show that it is expected to produce the same clinical result as the reference product in any given patient. Also, for products administered to a patient more than once, the risk in terms of safety and reduced efficacy of switching back and forth between an interchangeable product and a reference product will have been evaluated. In the US, an interchangeable product may be substituted for the reference product without the involvement of the prescriber, consistent with state pharmacy laws.5
  • Non-comparables
    Biologic medicines that are marketed in some countries, that are designed to act like an approved biologic medicine but that have not been evaluated using the rigorous regulatory pathway required for biosimilars. Also known as ‘biocopies’, ‘biomimics’, ‘intended copies’ and ‘nonregulated biologics’.6
  • Reference product
    A previously approved product used as the comparator for head-to-head comparability studies with the biosimilar in order to evaluate similarity in terms of quality, safety, and efficacy. A reference product is sometimes referred to as the innovator or originator product.2
  • Small molecule generic
    A small-molecule, chemically synthesized drug that uses the same active ingredient, strength, dosage form, route of administration and conditions of use as the reference product on which it is based.7
  • Totality of evidence
    The totality of data and information used by regulatory authorities to evaluate a biosimilar for market approval. Included are structural and functional characterization, nonclinical evaluation, PK and PD data, immunogenicity data and the results of comparative clinical studies.3


  1. Sekhon, et al. Biosimilars. 2011:1;1-11
  2. Desanvicente-Celis, et al. Immunotherapy. 2012;4:1841-1857.
  3. USFDA. Scientific Considerations in Demonstrating Biosimilarity to a Reference Product. 2015.
  4. Markus, et al. BioDrugs. 2017;31:175-187.
  5. USFDA. Biosimilar and Interchangeable Products. 2021.
  6. Dörner, et al. Nat Rev Rheumatol. 2015;11:713-724.
  7. USFDA. Generic Drug Facts. 2021.