Key Points

• Practitioners should identify all indefiniteness grounds — including those apparent from the face of the patent — at the earliest disclosure deadline to avoid forfeiture under local patent rules.
• Court denied motion to amend invalidity contentions to add new indefiniteness theories 20 months after original service, finding lack of good cause under District of New Jersey Local Patent Rule 3.7.
• Court's prior deferral of indefiniteness issues to summary judgment during Markman did not excuse untimely disclosure.

Disclose Theories at the Outset

A recent decision by U.S. Magistrate Judge Jessica S. Allen underscores the importance of developing and disclosing theories relating to patent invalidity and infringement at the outset of litigation to avoid running afoul of the Local Patent Rules of the District of New Jersey.

In Epitopix LLC v. Zoetis, Inc., Judge Allen denied a motion for leave to amend invalidity contentions filed 20 months after service of the original invalidity contentions seeking to add two new indefiniteness theories based upon the plain language of the patent at issue.

The Local Patent Rules of the District of New Jersey dictate the scope and pace of patent litigation and may be enforced strictly. They “are designed to require the parties to crystallize their theories of the case early in the litigation and to adhere to those theories once they have been disclosed.” Amgen Inc. v. Kashiv Biosciences LLC, 2019 WL 5445974, at *1 (D.N.J. Oct. 24, 2019).

Rule 3.3(d) mandates disclosure of invalidity contentions relatively early in litigation proceedings, typically within two months of the initial scheduling conference. Relevant to Epitopix, among other requirements, a party’s invalidity contentions must disclose “[a]ny grounds of invalidity based on . . . indefiniteness under 35 U.S.C. § 112(b)[.]”

Critically, Local Patent Rule 3.7 provides that invalidity contentions may be amended “only by order of the Court upon a timely application and showing of good cause.” (emphasis in original).

Not a Straitjacket

Judge Allen noted that while the DNJ’s Local Patent Rules are not “a straitjacket into which litigants are locked from the moment their contentions are served,” leave to amend invalidity contentions is not liberally granted “because the philosophy behind amending claim charts is decidedly conservative and designed to prevent the shifting sands approach to a party’s contentions.” Decision at 4 (cleaned up).

Leave to amend contentions may be granted upon a showing of three things: “(1) the application is timely; (2) there is good cause for the amendment; and (3) the adverse party will not suffer undue prejudice if leave to amend is granted.” Decision at 4.

Judge Allen found that Zoetis’ supplemental invalidity contentions were not timely disclosed, indicating a lack of good cause for the amendment. Accordingly, she did not reach the question of prejudice to Epitopix in denying Zoetis’ motion.

Zoetis disclosed its invalidity contentions in December 2023, including several theories of indefiniteness. The case proceeded, with the Court issuing a Markman opinion and order in January 2025 that deferred questions of indefiniteness until summary judgment. Zoetis subsequently served purported supplemental invalidity contentions in May 2025, including two new indefiniteness theories based on the plain language of the patent. Epitopix objected to these as untimely, and Zoetis ultimately moved to amend its invalidity contentions to add the new theories in August 2025.

Judge Allen began her analysis by noting, “[i]ndefiniteness is a relatively basic concept — that is, a patent is supposed to identify to a person of skill in the art the distinction between what is claimed and what is not.” Decision at 8. Judge Allen determined that Zoetis’ new indefiniteness theories were “based on the plain language” of the patent and found that Zoetis “provide[d] no explanation as to why it could not, despite exercising due diligence, assert these completely new indefiniteness arguments in its original contentions.” Decision at 8.

Zoetis’ motion — filed 20 months after service of its original invalidity contentions —was not diligently pursued and therefore lacking in good cause, Judge Allen found, holding that “it appears that Defendant has simply re-evaluated the asserted claims and seeks to add new arguments. This amounts to a litigation strategy, which is not akin to showing good cause.” Decision at 8.

Judge Allen succinctly dismissed Defendant’s assertion that its indefiniteness theories were submitted within the “spirt” (though not the letter) of the Local Patent Rules as the Court had deferred indefiniteness considerations to the summary judgment stage during Markman, holding “that is a non sequitur, as timeliness is measured by a party’s diligence … And here, Defendant has not been diligent because Defendant’s proposed new indefiniteness positions are not based on the substance of the Court’s Markman Opinion, but rather, are grammatical and based on the face of the patent that has been available for years.” Decision at 9.

The Takeaway

This decision is a timely reminder that indefiniteness theories of invalidity based on the plain language of a patent should usually be disclosed with a party’s original invalidity disclosures under the DNJ’s Local Patent Rules. Moreover, where new indefiniteness theories are based on the plain language of the patent, parties are likely to face an uphill battle to have an amendment granted.

Paul W. Kalish and Jonathan J. Madara are members of the IP Litigation team in Fox Rothschild’s Princeton, NJ office and write about patent litigation decisions in the District of New Jersey. Contact Paul at pkalish@foxrothschild.com or 609.895.6751 and Jonathan at jmadara@foxrothschild.com or 609.844.7428.

This information is intended to inform firm clients and friends about legal developments, including the decisions of courts and administrative bodies. Nothing in this alert should be construed as legal advice or a legal opinion. Readers should not act upon the information contained in this alert without seeking the advice of legal counsel. Views expressed are those of the authors and not necessarily this law firm or its clients.