Key Points

• Later-filed, later-expiring patents and applications may serve as an OTDP reference.
• Preventing harassment by multiple assignees is a legitimate independent rationale for OTDP, even absent improper patent term extension, but the ARP invited the Federal Circuit to provide clarification.
• The Allergan exception still can be narrowly applied. It requires first actual filing date in the patent family, common priority date with the reference patent, and first-issued status.
• Terminal disclaimers to later-filed, later-expiring patents and applications may be unavailable (due to lack of common ownership in collaborations) or undesirable (where the earlier application has accumulated significant PTA that would be lost).

The Appeals Review Panel (ARP) of the U.S. Patent and Trademark Office’s (USPTO) Patent Trial and Appeal Board (PTAB) recently issued a precedential decision on a sua sponte rehearing of Ex parte Baurin, reinstating the Examiner’s obviousness-type double patenting (OTDP) rejections of claims 1-18 of U.S. Application No. 17/135,529 (the ‘529 application). The August 6, 2026, decision reaffirms existing examination practices and has significant implications for patent owners and applicants with large patent estates, developing improvement technologies or navigating complex ownership arrangements.

Here's what patent owners and applicants need to know.

Background

Obviousness-type double patenting is a judicially created doctrine designed to prevent a patentee from unjustifiably extending patent exclusivity by obtaining multiple patents on patentably indistinct inventions. The doctrine originated under the pre-1995 patent term framework, when patent term ran seventeen years from issuance. Under that system, a later-issued patent generally expired later, and applicants could potentially extend their monopoly well beyond the original patent term by filing continuation applications claiming obvious variants of the same invention. The Uruguay Round Agreements Act (URAA), effective June 8, 1995, changed patent term to twenty years from the earliest effective filing date, which meant that related applications sharing a common priority date would generally expire on the same date. While this change reduced the risk of improper term extension within patent families, the OTDP doctrine remains relevant where patents have different expiration dates—whether due to different patent term filing dates or patent term adjustment (PTA) awarded to compensate for USPTO examination delays.

OTDP may be overcome by a terminal disclaimer, which requires the applicant to disclaim any patent term extending beyond the expiration of the reference patent and to maintain common ownership between the patents. This creates particular challenges for improvement technology: later-filed improvement claims will often render earlier-filed foundational technology claims obvious under OTDP analysis, which may force applicants to file terminal disclaimers that forfeit accumulated PTA and impose common ownership requirements. In collaborative research settings or where inventor mobility is common, the common ownership requirement may be impossible to satisfy, leaving applicants with no viable path to overcome the OTDP rejection.

Procedural History

Claims 1-18 of the ‘529 application are directed to antibody-like binding proteins comprising two polypeptide chains that form two antigen binding sites with certain structures. The claims were rejected for OTDP as unpatentable over U.S. Patent No. 10,882,922 (the ‘922 patent) in view of US2009/0162359 (“Klein”). The ’922 patent claims trispecific antibody-like binding proteins.

The ‘529 application was filed on December 28, 2020, but claims priority through a chain of continuation applications to a patent term filing date of March 28, 2012, resulting in a 20-year statutory term expiring on March 28, 2032. The ‘922 patent has an actual and patent term filing date of April 13, 2017, with 70 days of patent term adjustment, resulting in an expiration date of June 22, 2037.

The PTAB initially sided with the applicant on Nov. 8, 2024, finding that the ‘922 patent could not serve as a proper OTDP reference because it was later-filed and later-expiring. The PTAB relied on Allergan USA, Inc. v. MSN Laboratories Private Ltd., 111 F.4th 1358 (Fed. Cir. 2024), which held that “a first-filed, first-issued, later-expiring claim cannot be invalidated by a later-filed, later-issued, earlier-expiring reference claim having a common priority date.”

The PTAB acknowledged that the facts differed from Allergan because the ‘529 application and ‘922 patent do not share a priority date or come from the same patent family, but found Allergan’s “reasoning compelling.” Citing Allergan, the PTAB described the fundamental purpose of OTDP as “to prevent patentees from obtaining a second patent on a patentably indistinct invention to effectively extend the life of a first patent.” Applying that reasoning, the PTAB concluded that the ‘529 application would be the “first patent” and “not a second, later expiring patent for the same invention.”

The Examiner requested rehearing, which the PTAB denied on December 18, 2025. On March 5, 2026, USPTO Director John Squires sua sponte convened an ARP to review the PTAB’s decision.

The ARP Decision

The ARP found that Allergan was not applicable to the facts of this appeal. The ARP explained that “first-filed” under Allergan means actual filing date rather than patent term filing date. The ‘529 application fails all three Allergan criteria: it does not have the first actual filing date in its patent family, does not share a common priority date with the ‘922 patent, and is not “first-issued.” Thus, Allergan’s narrow exception does not apply.

The ARP held that the PTAB erred in dismissing the anti-harassment rationale as inadequate to support the Examiner’s OTDP rejections. The OTDP doctrine has two justifications: (1) preventing unjustified timewise extension of patent term, and (2) preventing harassment by separate owners asserting essentially the same patented invention. The ARP found that Federal Circuit precedent — including In re Fallaux, 564 F.3d 1313 (Fed. Cir. 2009); In re Hubbell, 709 F.3d 1140 (Fed. Cir. 2013); and In re Cellect, 81 F.4th 1216 (Fed. Cir. 2023) — supports OTDP rejections even absent term extension concerns.

Notably, the ARP acknowledged some uncertainty. The panel stated that if “the Federal Circuit’s precedents should not be read to permit OTDP rejections based on the anti-harassment rationale where no term-extension concern is apparent, the Office would welcome that clarification from the court.” This issue is currently before the Federal Circuit in In re Ablynx N.V., Appeal No. 26-1333 (sub nom Ex parte Baumeister).

The ARP also proposed a contingent framework for OTDP examination, should the Federal Circuit clarify that anti-harassment cannot be a sole rationale for an OTDP rejection. Under this framework, examiners would use patent term filing dates as a surrogate for expiration dates: if a putative OTDP reference has a later patent term filing date than the patent term filing date of the application under examination, the OTDP analysis under the term-extension rationale would end. Within the same patent family, examiners would focus on actual filing dates, permitting OTDP rejections of later-filed applications based on earlier-filed parent applications, but not the reverse.

Takeaways

Protection against OTDP rejection under Allergan remains available, but only under narrow circumstances: within a single patent family where the claims under examination are first-filed, first-issued, and later-expiring. However, because continuation and divisional applications are often filed shortly before issuance of a first patent in a family, this scenario is unlikely during original examination and more likely during reexamination or reissue proceedings.

Following the ARP decision, applicants should expect OTDP rejections based on commonly owned, later-filed, later-expiring patents and applications — even those outside the same patent family.

While terminal disclaimers may be filed in the earlier-filed application (which typically would not affect its term), terminal disclaimers may be unavailable due to lack of common ownership (common in collaborations) or undesirable where the earlier application has accumulated significant PTA that would be lost. Drafting claims to avoid obviousness overlap is an option, but this may be particularly difficult for improvement technology, where narrowing foundational technology claims may sacrifice broader scope to which the applicant would otherwise be entitled. Given the pending Ablynx appeal, applicants facing OTDP rejections based solely on the anti-harassment rationale — without a term extension concern — may consider deferring the filing of a terminal disclaimer until the Federal Circuit provides further guidance.

For more information, please contact Eileen S. Sun at esun@foxrothschild.com or another member of Fox Rothschild’s Intellectual Property Department.

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 author(s) and not necessarily this law firm or its clients. Prior results do not guarantee a similar outcome.