(Reuters) -Swiss generic drug manufacturer Sandoz (SIX: SDZ ) said on Monday it had filed an antitrust lawsuit in the United States against Amgen (NASDAQ: AMGN ) over the alleged entrenchment of the market position of its blockbuster medicine, Enbrel (etanercept).

Sandoz alleges Amgen blocked competition from more cost-effective biosimilar competitors, including Sandoz etanercept biosimilar, Erelzi, by unlawfully purchasing and using certain patent rights to entrench its dominant market position.

Amgen did not immediately reply to a request for comment.

Submitted on Friday, Sandoz’s lawsuit alleged Amgen has used a "thicket of patents" to protect its monopoly for Enbrel through 2029 in violation of U.S. federal antitrust law.

Filed in a Norfolk, Virginia, federal court, it accused Amgen of "reaping billions in profits while denying purchasers and patients access to the lower prices they would have paid in a competitive market, where Sandoz was able to launch."

Sandoz in its lawsuit said it "continues to lose out on millions of dollars in sales each month that it remains sidelined by Amgen’s illegal activity."

In 2024, Enbrel generated $3.3 billion in revenue in the United States, Sandoz said. Etanercept is used to treat a range of inflammatory diseases, including rheumatoid arthritis.

Basel-based Sandoz received U.S. Food and Drug Administration approval for Erelzi in 2016, the same year the company launched the medicine in Europe.

Sandoz wants an injunction to prevent Amgen from using patent rights to block biosimilar competition and allow Sandoz to launch Erelzi as soon as possible. It is also seeking damages.