Americans with psoriasis and rheumatoid arthritis will have to wait much longer for low-priced copycat versions of their weekly Enbrel injections. Amgen (NASDAQ:AMGN) won an appeals court ruling on Wednesday that will block the sale of Erlelzi from Novartis (NYSE:NVS) and all other biosimilar versions of Enbrel until 2029 at the earliest.

Enbrel is a tumor necrosis factor (TNF) inhibitor that earned its first FDA approval all the way back in 1998. A company called Immunex bought patents to Enbrel from Roche, and then Amgen bought Immunex in 2002.

How to earn three decades of market exclusivity

After Amgen acquired Immunex, the biotech filed new patents regarding Enbrel's composition of matter and manufacturing process that mimic the patents that Immunex had already acquired from Roche.

Cash money and prescription drugs.

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There are rules that prevent companies from simply filing identical patents to extend market exclusivity. Amgen got around them by successfully arguing that Roche retained significant ownership of its Enbrel patents when Amgen bought Immunex.

More growth ahead

Competition with Erlizi and other Enbrel biosimilars would have made it tough for Amgen to continue growing. In the first quarter of 2020, U.S. Enbrel sales worked out to 19% of Amgen's total product revenue for the period.

Biosimilar competition abroad has decimated U.S. sales of Enbrel outside of the U.S., but it's still a success in its domestic market. U.S. Enbrel sales last year came in at $5.1 billion last year, and it's on pace to generate another $4.5 billion in 2020.