Erelzi, Enbrel, and the Wait That Isn't Over

Erelzi - Sandoz's biosimilar of Enbrel - received FDA approval in August 2016. As of April 2026, it hasn't launched in the US. The same drug has been on sale in Europe since June 2017.

If Erelzi launches when Enbrel's US patent cliff arrives in April 2029, it will have been fully developed, FDA-approved, and legally unsellable in the US for roughly 12.6 years. That's double the Amjevita wait.

But the 2029 date has been contested. An antitrust challenge was dismissed in February 2026, and Sandoz is now appealing to the Fourth Circuit. The base case has solidified, but the story isn't closed.

The drug

Enbrel (etanercept) was FDA-approved in November 1998. It was one of the earliest TNF-inhibitor biologics - same therapeutic class as Humira, different molecular structure (a fusion protein rather than a monoclonal antibody). It became a blockbuster almost immediately.

In July 2002, Amgen acquired Immunex - the company that developed Enbrel - for approximately $16 billion. At the time it was the largest biotech M&A deal ever. Enbrel was the prize asset. By 2017 its US sales had reached $5.4 billion a year at peak.

Under the original Immunex-era patents, Enbrel's US exclusivity was expected to end around 2012. Biosimilar developers - most notably Sandoz - built programs targeting that window.

Then the window moved.

How a 2012 cliff became a 2029 cliff

In the early 1990s, Roche scientist Werner Brockhaus filed patent applications covering the TNF receptor fusion protein construct - the molecular architecture that makes Enbrel what it is. These applications entered the USPTO examination process and stayed there. For roughly two decades.

This matters because of a timing rule. Under the patent term laws in effect when Brockhaus filed (pre-1995), US patents received 17 years of protection from the date of issuance - not from the date of filing. A patent filed in 1991 and issued in 1993 would expire in 2010. But a patent filed in 1991 and not issued until 2011 wouldn't expire until 2028.

The Brockhaus applications fell into the second category. The USPTO didn't issue them until November 2011 - as US 8,063,182 and its companion US 8,163,522. The 17-year clock started then. Expiry: 2028-2029.

Nobody at Amgen "extended" the patents. The extension was a consequence of how long prosecution took at the Patent Office, combined with the pre-1995 term rules. But who controlled the patents when they finally issued - that was a strategic decision:

• 1999: Immunex (pre-Amgen) licensed the still-pending Brockhaus applications from Roche.
• 2002: Amgen acquired Immunex, inheriting that license.
• 2004: Amgen paid Roche a one-time payment for an exclusive, fully paid-up license - ensuring that when the patents eventually issued, only Amgen could enforce them.
• 2011: The patents issued. Amgen held sole control.

The industry had priced Enbrel's exclusivity for a ~2012 expiry based on the original Immunex-era patents. The Brockhaus patents pushed the effective cliff to April 2029 - an additional 17 years of US protection. A 2020 House Oversight Committee report documented the full patent history and its effect on Enbrel pricing.

The chart above shows a drug declining without any biosimilar competition. Enbrel is a 1998 drug competing against newer biologics - Rinvoq (an oral JAK inhibitor), Skyrizi and Tremfya (IL-23 inhibitors with better efficacy data in psoriasis), and Cosentyx (IL-17). The market that Erelzi was built to enter is shrinking while it waits.

The first legal round (2016-2020)

Sandoz received FDA approval for Erelzi in August 2016 and planned to launch. Immunex (with Amgen as parent and exclusive licensee) sued, asserting the Brockhaus patents.

Sandoz's central defense was Obviousness-Type Double Patenting (OTDP) - arguing that if Immunex effectively controlled both the earlier expired patents and the newer Brockhaus patents, the newer ones should be invalidated because they protected the same invention beyond its originally expected term.

After a two-week bench trial in September 2018, the District Court ruled for Immunex/Amgen in August 2019. The Brockhaus patents were held valid. The Federal Circuit affirmed in a 2-1 decision on July 1, 2020, finding that the exclusive license did not amount to common ownership in the legal sense. Judge Reyna dissented, arguing the economic reality was different from the contract language.

Erelzi stayed shelved. A second Enbrel biosimilar - Eticovo, from Samsung Bioepis - received FDA approval in April 2019 and joined Erelzi on the shelf.

Meanwhile, in Europe

Enbrel's patent situation in Europe was different. Sandoz launched Erelzi in Europe in June 2017 - same drug, same factories, different patent landscape. It also launched in Canada and other markets well ahead of any US availability.

As of April 2026, the same molecule has been available outside the US for nearly a decade.

The second legal round (2025-present)

In April 2025, Sandoz filed a new lawsuit against Amgen - this time in the Eastern District of Virginia, with a completely different legal theory.

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Sandoz isn't attacking the Brockhaus patents themselves - they lost that battle in 2020. The new case targets the 2004 transaction in which Amgen acquired exclusive rights to the patents from Roche. The complaint argues that by acquiring exclusive rights, Amgen removed a potential source of biosimilar licensing and consolidated monopoly control over the enabling IP for its own product - an unlawful horizontal restraint under antitrust law.

In October 2025, the court denied Amgen's motion to dismiss, drawing a distinction: patent prosecution and enforcement is protected activity under the Noerr-Pennington doctrine, but patent acquisition is a private commercial act - not immune from antitrust scrutiny. The case appeared to be heading to discovery.

Then the court reversed course. On February 17, 2026, the District Court dismissed Sandoz's antitrust claim and entered judgment in favor of Amgen. Sandoz lost at the trial court level.

On March 16, 2026, Sandoz filed an appeal with the US Court of Appeals for the Fourth Circuit. The case is now before the appellate court.

What happens next

The district court dismissal strengthened the base case - April 2029. But the Fourth Circuit appeal keeps the question open. Here's how it could play out:

Why this matters beyond Enbrel

The Humira story showed that patent settlements create predictable shelving periods. The Enbrel story shows something different: patent acquisition - a company buying exclusive rights to a patent family covering its own product - creates a different kind of shelving, one that's now being tested under antitrust law for the first time.

For anyone modeling post-cliff revenue on biologic franchises:

• Patent cliff dates from public sources are the best starting point, but they're not immutable. Active litigation can move them earlier.
• Track antitrust litigation separately from patent litigation. Different legal theories, different time horizons, different burdens of proof.
• Shelved biosimilar counts are a leading indicator of motivated challengers. Sandoz has a decade of invested capital riding on getting to market.

Fourteen biosimilars are currently shelved across the industry. This case will influence how the next round of shelving periods plays out.