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Understanding Biosimilars and the FDA Approval Process

As more and more biosimilar medications come to market it is key to understand what is required for these drugs to be approved by the FDA.

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In this edition of the Clinical Corner, we will review the approval process for biosimilar medications.

Biosimilar agents are large, complex molecules. They may have active ingredients that are not identical to a referenced brand name product, a medication approved for use by the FDA. Active ingredients may include proteins or monoclonal antibodies that are often produced through biotechnology processes involving microorganism or plant/animal cells.  On the other hand, generic drugs are small molecules and are required to have the identical active ingredient(s) to the brand name reference product.

To be approved by the FDA, biosimilar products are compared to a reference product. The biosimilar must show it is both “highly similar” and has “no clinically meaningful differences” in both safety and efficacy. A product is determined to be “highly similar” after extensive testing to analyze the structure and function of both the reference product and biosimilar with regards to biological activity, chemical identity, and purity. It is acceptable for there to be differences regarding inactive ingredients between the two products as long as the stipulations above are met. Additionally, the biosimilar and reference product could have slight differences in other areas but must be consistent with the same lot-to-lot variance allowed by the FDA for the reference product. The ability to have different inactive ingredients and lot-to-lot variances are two of the few similarities between approval processes for generic drugs and biosimilars.

In order to demonstrate “no clinically meaningful differences”, biosimilars are evaluated on safety, purity, potency, and effectiveness. Additional in-depth studies are done on the pharmacokinetic, pharmacodynamic, and clinical immunogenicity of the proposed biosimilar. Each study is completed to help ensure the biosimilar will work as the reference product does within the body. Generic drugs must also go through bioequivalence testing which shows the medication is absorbed at the same rate and to the same extent as the brand name counterpart. Due to the complexity of biosimilars, bioequivalence testing cannot be performed in the same manner.

As biosimilars are not generic drugs, in most cases they cannot be substituted for the reference product. If the biosimilar manufacturer performs additional testing, including switching studies, the biosimilar could be deemed an interchangeable product by the FDA. In this case, the product is now labeled as interchangeable with the reference product and is considered substitutable.  Currently there are no biosimilar agents that have achieved this designation.  It is also important to mention that at this time, some states still have not formally implemented substitution rules surrounding biosimilar agents, even if deemed interchangeable.

Below are some of the more common biosimilar agents that may be obtained through the prescription drug benefit along with the corresponding reference product.


Reference Product

Therapeutic Use

Retacrit® Procrit®, Epogen® Anemia
Zarxio®, Nivestym® Neupogen® Neutropenia prophylaxis
Fulphila®, Udenyca® Neulasta® Neutropenia prophylaxis
Inflectra®, Ixifi®, Renflexis® Remicade® Systemic inflammatory conditions
Truxima® Rituxan® Cancer / Autoimmune conditions


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