OMI Urges Appeals Court to Allow Antitrust Challenge to Amgen’s Extension of Enbrel Monopoly
Amicus brief argues monopolists cannot use acquisitions of pending patents to shut out rivals and keep drug prices high
The Open Markets Institute filed an amicus brief in the U.S. Court of Appeals for the Fourth Circuit urging the court to allow an antitrust lawsuit, CareFirst v. Amgen, that challenges Amgen’s use of acquired patent rights to extend its monopoly over the blockbuster drug Enbrel.
Enbrel, a biologic drug used to treat rheumatoid arthritis and other autoimmune conditions, generates billions of dollars in annual revenue for Amgen. The lawsuit alleges that, two years after obtaining the rights to Enbrel through its 2002 buyout of Immunex, Amgen effectively acquired pending patent applications related to the drug from Roche. These patent rights were subsequently used to prevent lower-cost biosimilar competitors from entering the market until 2029.
Open Markets argues that this alleged strategy can constitute illegal monopolization under Section 2 of the Sherman Act. This antimonopoly provision of the prohibits companies from acquiring or maintaining monopoly power through exclusionary conduct, which includes acquisitions of assets such as patents and pending patents.
“Patent law is supposed to reward innovation, not provide a playbook for monopolists to buy up potential threats and perpetuate their dominance,” said Tara Pincock, Policy Counsel at the Open Markets Institute. “When a dominant pharmaceutical company acquires patent rights and uses them to extend an existing monopoly, antitrust law has a critical role to play. Patients should not be forced to pay monopoly prices for years longer because a powerful corporation found another way to block competition.”
If it had retained the patent rights, Roche likely would have licensed them to other companies or used them to enter the Enbrel market itself. Amgen instead allegedly acquired those rights and used them to erect barriers against biosimilar competitors, extending its monopoly until 2029. The resulting exclusion has cost patients and payors billions of dollars in potential savings, the brief argues.
A federal district court rejected Amgen’s attempt to dismiss the lawsuit in September 2025. Amgen is now asking the Fourth Circuit to reverse that ruling and terminate the case. Open Markets urges the appeals court to affirm the lower court and allow the antitrust challenge to proceed.
As the brief explains, the Supreme Court has recognized that patent rights cannot be used to achieve objectives prohibited by antitrust law, and courts have recognized that acquisitions of patents and transfers of pending patent applications can trigger Sherman Act liability.
“Amgen’s alleged conduct illustrates exactly why courts must look at how monopolists actually maintain their power,” said Sandeep Vaheesan, Legal Director at the Open Markets Institute. “A monopolist should not be able to purchase assets that could otherwise enable competition and use them to build a moat around its monopoly. Antitrust law has long prohibited acquisitions used to exclude rivals, and pending patent rights should be no exception.”
The brief further argues that pending patent applications have genuine economic and competitive significance even before patents are formally granted. Companies license pending patents and use them as collateral to obtain credit precisely because they may ultimately confer the power to exclude competitors. In Amgen’s case, the acquisition allegedly paid off spectacularly: the applications ultimately produced valuable patents that helped keep biosimilar competitors out of the Enbrel market for years.
Open Markets is asking the Fourth Circuit to affirm the district court’s order denying Amgen’s motion to dismiss and allow the plaintiffs’ antitrust case to move forward.