A Blog About Intellectual Property Litigation and the District of Delaware


Entries for tag: Estoppel

A Bit Of Estoppel Lore

Nathan R. Hoeschen, Aug. 7, 2025
Estoppel

Estoppel is a word rarely used by the layman. It is a hothouse flower that seems able to grow only in the rarefied loam of the law, dying quickly when exposed to modern vernacular. \

But it was not always so. Like much legal jargon, it springs from old French, and in particular "estopail" which meant the plug you put in a barrels bunghole to prevent your wine from leaking out.

The more you know
The more you know Svetlana Gumerova, Unsplash

But I digress.

Today's opinion in Cognipower LLC v. Fantasia Trading LLC, C.A. No. 19-2293-JLH-SRF (D. Del.) dealt with a rather novel estoppel argument I hadn't seen before. The Defendant had filed multiple IPRs on the many asserted …

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Injunction Junction

Nathan R. Hoeschen, Feb. 13, 2025
Preliminary Injunction ANDA

I hope some of you saw the musical video Andrew posted yesterday before it was taken down in a copyright strike by the Prince Estate due to his eerily pitch perfect parody. The costumes alone were worth the price of admission.

Honestly the photo doesn't do it justice
Honestly the photo doesn't do it justice AI-Generated, displayed with permission

Hopefully tomorrow's video—Injunction Junction—fairs better.

Mallinkrodt Pharms. Ireland Ltd. v. Airgas Therapeutics LLC, C.A. No. 22-1648-RGA (D. Del. Feb 12, 2025). presented an interesting twist on the tried and true preliminary injunction formula.

The likelihood of success analysis was pretty standard (although it touched on one of my favorite issues—drug interaction). Ditto for irreparable harm, with the Court finding allegations of lost sales and …

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A Potential Signpost for Estoppel

Nathan R. Hoeschen, Sept. 29, 2022
Estoppel

The law is littered with reasonable people, and none of them do us much good. We have the reasonable person exercising ordinary caution (negligence). There's the reasonable person who attaches importance to the existence or nonexistence of a fact in determining his choice of action (materiality). Relevant to this blog post, and pictured below, we have the "skilled researcher conducting a diligent search" (estoppel).

Cookie the Pom, Unsplash

For those who haven't encountered this one in a while, this hypothetical skilled researcher is the measuring stick we use to determine whether a given reference could have reasonable been raised in an IPR and thus, whether an accused infringer is estopped from raising it in the district court.

As measuring …

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Judge Noreika Chooses a Side on IPR Estoppel: No Estoppel of Prior Art Products

Andrew E. Russell, July 12, 2022
IPR Estoppel Estoppel

Split
Bannon Morrissy, Unsplash

IPR estoppel can be kind of terrifying as an accused infringer in a patent action. The statute says that an accused infringer may not assert invalidity on a ground that it could have raised in the IPR; but you can't raise product prior art, so product prior art should be safe, right?

Nope. Courts have sometimes held that product prior art may still be estopped, if there is patent or written prior art that is sufficiently similar. See, e.g., Wasica Fin. GmbH v. Schrader Int’l, 432 F. Supp. 3d 448, 453 (D. Del. 2020) (holding defendant estopped from asserting product art where “all the relevant features” of the art were in a printed publication that could have been raised in an IPR).

As Judge Stark notes in Wasica, courts have gone both ways on this, with some estopping arguments based on product art where similar written or patent art could have been raised in an IPR, and others permitting those arguments.

On Friday, Judge Noreika chose a side in this split: no estoppel for prior art products ...

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Your IPR Succeeded? Congrats! Now Go to Trial on Infringement, But You're Estopped from Claiming Invalidity

Andrew E. Russell, Feb. 8, 2022
Collateral Estoppel IPR

PTAB trailhead
PTAB trailhead Joshua Sukoff, Unsplash

During some research the other day, I came across the below order that Judge Noreika issued last summer.

A defendant had moved in limine to exclude three of the four asserted claims of a patent from trial, after it prevailed on those claims in an IPR. Easy motion, right?

No. Judge Noreika held that, under Federal Circuit precedent, collateral estoppel does not prevent plaintiff from asserting those claims at trial until the decision is final. And the decision is not final until the appeal is exhausted:

Federal Circuit case law suggests that an IPR decision does not have preclusive effect until that decision is either affirmed or the parties waive their appeal …
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Chief Judge Connolly Denies Mostly-Unopposed Stay Pending CBM Review Because Defendant Refused to Consent to Statutory Estoppel

Andrew E. Russell, Jan. 17, 2022
CBM Estoppel

Stop Sign
Luke van Zyl, Unsplash

There are certain situations that come up over and over in patent cases. One of them is that a plaintiff will bring identical infringement suits against multiple defendants, and one of those defendants will then file an IPR or CBM proceeding before the patent office attacking the validity of the patents.

Under the America Invents Act, the filing party and any real party in interest are subject to estoppel. But unrelated defendants are not. The filing party will often move to stay the district court litigation. Generally speaking, parties with an instituted IPR or CBM review of all patents-in-suit often have pretty good chances of getting a stay.

So what happens when the defendants in …

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Judge Fallon Rejects Novel Attempt to Use Collatoral Estoppel to Invalidate Claims Based on IPR

Andrew E. Russell, Dec. 28, 2020
Collateral Estoppel Estoppel

Sierra Nevada Mountains
Sierra Nevada Mountains Alistair Corden, Unsplash

The defendant in M2M Solutions LLC v. Sierra Wireless America, Inc., C.A. No. 14-1102-RGA (D. Del.), argued that the PTAB's previous invalidation of several claims of the plaintiff's patents in an IPR meant that the plaintiffs were collaterally estopped from asserting the validity of the remaining claims—the claims that were not invalidated—at the district court.

Defendant argued that:

  • The Federal Circuit has held that collateral estoppel applies to IPR proceedings generally;
  • The Supreme Court has held that agency decisions may have preclusive effects during later court proceedings; and
  • The Federal Circuit has extended collateral estoppel effects to unajudicated claims when there were no material differences between those and …
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Fed. Cir. Improves Cost / Benefit Calculus for Defendants Joining IPRs

Andrew E. Russell, Sept. 24, 2020
Estoppel IPR

Previous equations for deciding whether to join an existing IPR
Previous equations for deciding whether to join an existing IPR Roman Mager, Unsplash

Today the Federal Circuit held that a party joining an existing IPR is not subject to estoppel on any grounds other than those that were actually raised. See the opinion below.

Before this, a plaintiff could argue that a defendant who joined an in-progress IPR was estopped on any anticipation or obviousness arguments that "reasonably could have [been] raised" in the IPR.

The Court here held, in short, that because a defendant joining an existing IPR is not allowed to add new grounds at all, it cannot be estopped except on those grounds actually raised.

It relied on the Facebook decision we talked about …

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Judge Noreika Rules that "Justice and Equity" Are Not Standalone Considerations in Collateral-Estoppel Analysis

Nathan R. Hoeschen, Sept. 17, 2020
Preclusion Estoppel

Plaintiff Estopped as Nearby District Moves to Overtake
Plaintiff Estopped as Nearby District Moves to Overtake Abed Ismail, Unsplash

Judge Noreika had a rare holding estopping a plaintiff from asserting the lone patent-in-suit patent due to collateral estoppel after trial.

The Court held a five-day bench trial in Biogen Int'l GmbH v. Amneal Pharms. LLC, C.A. No 17-823-MN in December 2019, dealing with a host on invalidity issues, including obviousness, enablement, and written description. The parties completed post-trial briefing in March 2020, and and a final opinion was thus expected in the not-too-distant future.

Unfortunately for Biogen, they also sued a different defendant, Mylan, in the Northern District of West Virginia on the same patent. That case went to trial in February 2020, on the sole …

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