The U.S. Supreme Court on Dec. 12 declined to hear an appeal from Canadian drugmaker Apotex Inc. in its legal battle against Amgen Inc. over whether all biosimilar manufacturers must wait 180 days after Food and Drug Administration approval before the firms can put their products on the U.S. market.

The court's rejection comes just days after the acting U.S. solicitor general urged the justices to take up another biosimilar lawsuit between Amgen and Sandoz Inc., a unit of Novartis AG. The court is not likely to reveal whether it will hear the Amgen-Sandoz case until January.

Both lawsuits center on the interpretation of the Biologics Price Competition and Innovation Act, a law passed by Congress in 2010 as part of the Affordable Care Act to give the FDA the regulatory authority to approve biosimilars, which are drugs meant to be cheaper versions of biological medicines.

The BPCIA set up certain processes under which biosimilar makers and brand-name drug manufacturers could resolve patent disputes, including disclosure and negotiation procedures, referred to as the "patent dance."

The BPCIA mandated that companies seeking approval from the FDA for a biosimilar "shall provide" no later than 180 days before the date of the first commercial marketing of its product a notice to the brand-name company.

In Amgen v. Sandoz, a three-judge panel from the U.S. Court of Appeals for the Federal Circuit in July 2015 ruled 2-1 that the patent dance was optional and that biosimilar makers could choose to not disclose their application and manufacturing details. The same panel, however, ruled 2-1 that when a biosimilar applicant does not dance, 180 days' notice of commercial marketing of biosimilars was mandatory and may be given only after FDA licensure.

But in Amgen v. Apotex, a different three-judge panel from the Federal Circuit this past July ruled that the post-approval 180-day notice of commercial marketing applies to all biosimilar makers, regardless of whether they turned over their application to the brand-name firms and engaged in the patent dance.

Apotex, which is seeking approval to market a version of Amgen's Neulasta, a leukocyte growth factor used to treat the depletion of white blood cells caused by cancer, had engaged in the patent dance, whereas Sandoz had not.

Sandoz gained FDA approval in March 2015 to market a version of Amgen's Neupogen, a shorter-acting version of Neulasta. Sandoz also is seeking U.S. approval to market a biosimilar of Neulasta, but was rejected on its first try.