The regulator granted a landmark approval to the copycat version of the already approved drug in the U.S., opening up the market to less expensive copies of biological products, while uncertainty related to a naming policy remains.

The FDA granted approval to Novartis unit Sandoz’s Zarxio for the same indications as its biosimilar, Amgen’s Neupogen.

The biosimilar product was approved under the Biologics Price Competition and Innovation Act of 2009, which was passed as part of the Affordable Care Act, and which created a pathway for biological products shown to be “biosimilar” to or “interchangeable” with an FDA-licensed biological product. The pathway allows the FDA to rely on existing scientific knowledge concerning the safety and effectiveness of an FDA-approved biological product – or reference product – and to clear a biosimilar biological product based on less than a full complement of product-specific preclinical and clinical data. Therefore, in order for a biosimilar product – which is generally derived from a living organism – to be granted approval, it must be demonstrated that it’s “highly similar” to a biological product that’s already approved, and that its safety and effectiveness are similar to those of the reference product.

Zarxio’s approval was based on the FDA’s review of evidence that included structural and functional characterization, animal study data, human pharmacokinetic and pharmacodynamics data, clinical immunogenicity data, and other clinical safety and effectiveness data – which showed Zarxio as biosimilar to Neupogen.

While the FDA cleared Zarxio as biosimilar, it did not approve it as interchangeable, meaning that a pharmacist can’t substitute it for the reference product without a health care practitioner being involved in the decision.

It’s worth noting that the FDA’s naming policy for biosimilar and other biological products remains uncertain. Since draft guidance hasn’t yet been issued, the FDA designated a placeholder nonproprietary name for Zarxio – “filgrastim-sndz” – specifying that the move doesn’t reflect its thinking on the issue.

As reported by the Wall Street Journal, “Biosimilars have been on sale in Europe since 2006, where their use has grown slowly, according to Michael Kleinrock, research director at the IMS Institute for Healthcare Informatics. Biosimilars have grabbed more than a 50 percent market share in the U.K. and Germany, and less than 40 percent in France.”

Kleinrock anticipates that biosimilar use in the U.S. will build at a similar pace, with the drugs eventually accounting for as much as 70 percent of prescriptions.