Biosimilar Listing in the Drug Compendia – GPI and GSN Identifiers

Currently, approved biosimilars are not interchangeable with the original biologics according to the FDA.  Drug compendia such as Medi-Span and FDB represent biosimilars as unique compared to the original biologic by classifying them in separate  GPIs and GSNs (clinical formulation IDs).  This is different than small molecule products where similar products (including B-rated products) are classified in the same GPI or GSN.

Future Scenarios

What will happen with interchangeable biosimilars when approved by the FDA?  Will Medi-Span and FDB group those in the same GPI or GSN as the original biologic?  Will they continue to differentiate interchangeable products in unique GPIs and GSNs?

If the drug compendia decided to keep the unique GPI and GSN classification for interchangeable biosimilars, PHSI would suggest the following methodologies to group biosimilars and innovator biologics together:

  • Using Medi-Span data, the GPI-8, Product Strength, and Dosage Form would group all biosimilars and the original biologic together.
  • Using FDB data, the Enhanced Therapeutic Classification (ETC), Strength, and Dosage Form groups all biosimilars and the original biologic together.

Another enhancement could be to create a common code linking interchangeable products (like the FDA’s Orange Book therapeutic ratings for small molecules).  This would differentiate biosimilars from interchangeable products within the proposed grouping methods above.


Contact PHSI with your questions and challenges with biosimilar drug compendia classification.


Published January 2019

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