Sandoz announced Thursday that the FDA has agreed to review its filgrastim biosimilar. Amgen’s Neupogen patent lapsed in December.

The branded biologic has wrangled close to $4 billion in sales between 2011 and 2013, but the performance has not been because of a competition-free bubble: Neupogen already competes with Amgen’s Neulasta, which has less-frequent dosing and a patent which runs into 2015. It also competes against Sandoz’s lookalike drug, which is already in 40 countries where it is known as Zarzio.

Sandoz said in its 2013 annual report that Zarzio was the first biosimilar to “overtake its reference product,” an achievement coupled with Zarzio being the first to push Chugai’s Granocyte from its market leader position.

Sandoz submitted its application through a process included in the FDA’s 2009 Biologics Price Competition and Innovation Act.