Why biosimilars need a different approach
Small-molecule generics are chemically identical to the originator. A biologic is a large, complex molecule made by living cells, so a copy can never be identical in every respect. The question is therefore not whether differences exist, but whether any differences matter for safety, purity and potency.
A stepwise, totality-of-evidence case
Regulators in India, Europe and the United States all describe a stepwise approach in which a detailed analytical comparison forms the foundation, followed by nonclinical and clinical studies as needed. The stronger and more complete the analytical similarity, the more targeted the later studies can be. In India, similar-biologics guidance issued by the CDSCO and the Department of Biotechnology sets out the framework.
What gets compared
- Primary structure: the amino-acid sequence, confirmed by mass spectrometry and peptide mapping.
- Higher-order structure: folding, using techniques such as circular dichroism, infrared spectroscopy, calorimetry and hydrogen-deuterium exchange mass spectrometry.
- Post-translational modifications: glycosylation, oxidation, deamidation and other changes that can affect activity or immunogenicity.
- Charge and size variants: ion-exchange and capillary methods for charge, size-exclusion and capillary electrophoresis for aggregates and fragments.
- Biological activity: binding assays (for example surface plasmon resonance or ELISA) and cell-based potency assays that reflect the mechanism of action.
- Impurities: host-cell proteins, residual DNA and process-related substances.
Why the reference product matters
Similarity is judged against the reference biologic, so reference lots must be sourced, stored and tested carefully. Several lots, covering different ages and sources, are measured to show how much the originator itself varies from lot to lot. The biosimilar is expected to sit within that natural variability for the attributes that matter most.
Tiering by criticality
Not every attribute carries equal weight. Attributes are ranked by their potential impact on clinical performance, and the strictest statistical comparison is applied to the most critical ones. Lower-risk attributes are compared with ranges or side-by-side data.
What sponsors should do early
- Secure enough reference lots, with documented history, before development accelerates.
- Qualify the analytical methods so that results are reproducible and sensitive enough to see real differences.
- Define critical quality attributes and acceptance ranges up front, not after the data arrive.
- Plan for forced-degradation and stability comparisons as well as release testing.
Analytical development is a core Theertha service. See our services or contact the team. This article is general information, not regulatory advice.
Frequently asked questions
Is a biosimilar the same as a generic drug?
No. A generic small-molecule drug is chemically identical to the originator. A biosimilar is a highly similar version of a complex biologic, shown through extensive comparison rather than being identical.
What is the role of the reference product?
It is the benchmark. Several lots are measured to define how much the originator naturally varies, and the biosimilar is compared against that range.
Does analytical similarity replace clinical studies?
Not entirely. It is the foundation, and the stronger it is, the more targeted the nonclinical and clinical studies can be, according to the applicable regulatory guidance.
General information for readers in biopharmaceutical development; not regulatory or medical advice.