While small molecule drugs are ideal for generics replication, biological drugs are not so simple. Biological drugs are usually large, complex molecular structures derived from or produced through a living organism, making them very difficult to replicate.

Standard methods for assessment of bioequivalence for regulatory approval of generic drug products are not appropriate due to some fundamental differences between small molecule generics and large molecule biosimilar products.

Compared with small molecule generic drug products, more stringent assessment of safety, purity and potency is required to show that a biosimilar is not clinically different from the reference biological product.

Although the FDA draft guidances did provide some insights regarding the assessment of biosimilarity of follow-on biologics, many scientific issues such as the definition of highly similar, criteria for biosimilarity, the feasibility of the stepwise approach, statistical tests for comparability in quality attributes, and the assessment of totality-of-the-evidence still remain unresolved for meeting regulatory expectations within the US. With respect to interchangeability of biosimilars with their reference products, in practice, it is difficult, if not impossible, to demonstrate the expected ‘same clinical result in any given patient’. However, it is possible to demonstrate ‘same clinical result in any given patient with certain assurance’.

In fact, many of the scientific factors and practical issues regarding the assessment of biosimilarity and interchangeability of biosimilars still remain unresolved within the US, and more research on these topics is needed.

In the two articles that follow, an overview of current criteria, study design and statistical methods for evaluation of biosimilarity and interchangeability for biosimilar products is given.

Conflict of interest
The authors declared that there were no conflicts of interest.

Editor’s comment
Readers interested to learn more of the issues of biosimilarity and interchangeability are invited to visit www.gabi-journal.net to view the following peer reviewed article published in GaBI Journal:

Assessing biosimilarity and interchangeability of biosimilar products under the Biologics Price Competition and Innovation Act

If you are interested in contributing a research article in a similar area to GaBI Journal, please send us your submission here.

Professor Shein-Chung Chow is a member of the International Editorial Advisory Board of GaBI Journal, an expert in bioavailability/biosimilarity and bioequivalence; and is the Guest Editor of the Special Issue (educational editorial series) on 'Biosimilarity and Interchangeability' currently under production by GaBI Journal, contact us for more information on this Special Issue.

Related articles

Assessment of interchangeability under the BPCI Act

Assessment of biosimilarity under the BPCI Act

References
1.  GaBI Online - Generics and Biosimilars Initiative. FDA finally issues draft biosimilar guidance [www.gabionline.net]. Mol, Belgium: Pro Pharma Communications International; [cited 2013 Jan 24]. Available from: www.gabionline.net/Guidelines/FDA-finally-issues-draft-biosimilar-guidance
2.  Chow SC, Ju C. Assessing biosimilarity and interchangeability of biosimilar products under the Biologics Price Competition and Innovation Act. Generics and Biosimilars Initiative Journal (GaBI Journal). 2013;2(1):20-5. doi: 10.5639/gabij.2013.0201.004

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