What Are Biosimilars?

A biosimilar is a biological product that is developed to be similar to an already FDA-approved biologic, known as the reference product. It can be tempting to think of a biosimilar as a “generic” version of the reference product. However, there are many important differences between biosimilars and generic versions of conventional medications (generic drugs).

A generic drug is chemically identical to its brand-name counterpart—an exact copy. The generic drug and brand-name drug have the same active ingredient, dosage form, safety profile, strength, route of administration, performance characteristics, and intended use. Accordingly, the brand-name drug and generic drug are considered to be bioequivalent.

A biosimilar is not an exact duplicate of another biologic. There is a degree of natural variability in all biological products; it is not possible to generate a precise copy of a product that comes from living cells. All biologics—including reference products—show some batch-to-batch variation.

A biosimilar may have a different structure than the reference product, but the active substances are essentially the same in molecular and biological terms. This means that there are no clinically meaningful differences between the biosimilar and reference product in terms of safety or effectiveness. Only minor differences in clinically inactive components are allowable.

The first biosimilar product in the United States, Zarxio, was approved in March 2015 and marketed in September 2015. Zarxio (filgrastim-sndz) is a biosimilar of Neupogen (filgrastim), a medication that helps to reduce the risk of infection in patients with certain types of cancer who are receiving chemotherapy that decreases the number of white blood cells. All biosimilar products that have been approved in the United States are listed in this table. More than 50 biosimilar products currently are in development.