Double Patenting, PTA, and Patent Families: What Cellect and Allergan Mean for Your Portfolio

Obviousness-type double patenting (ODP) can silently eliminate patent term adjustment (PTA) from patents in a family — even PTA that was legitimately earned through years of USPTO delay. Since the Federal Circuit's 2023 decision in In re Cellect, LLC, ODP analysis must account for each patent's PTA-adjusted expiration date, not just the base 20-year term. And since the 2024 decision in Allergan v. MSN Labs, a critical safe harbor exists: a first-filed, first-issued, later-expiring parent patent cannot be invalidated via ODP by a later-filed, later-issued, earlier-expiring child. Together, these decisions fundamentally reshape how patent families should be prosecuted and managed.

Scope: This article covers the intersection of ODP and PTA under current US patent law, focusing on the Cellect and Allergan decisions and their practical implications for prosecution strategy. For background on terminal disclaimers, see our terminal disclaimers guide. For PTA fundamentals, see our PTA vs PTE comparison.

What Is Obviousness-Type Double Patenting?

ODP is a judicially created doctrine rooted in 35 U.S.C. § 101, which provides that an inventor may obtain "a patent" for an invention. ODP prevents a patentee from obtaining a second patent with claims that are not patentably distinct from those of a first patent, effectively extending patent protection beyond the term of the first patent.

When an examiner issues an ODP rejection, the applicant can typically overcome it by filing a terminal disclaimer under 35 U.S.C. § 253, agreeing that the later patent will expire no later than the reference patent and will be enforceable only under common ownership. But as the Cellect and Allergan decisions show, the timing and direction of that terminal disclaimer — and whether one is needed at all — depend critically on each patent's PTA.

Cellect (2023): ODP Must Account for PTA-Adjusted Expiration

In In re Cellect (Fed. Cir. 2023), the Federal Circuit held that ODP analysis must be based on each patent's expiration date after PTA has been added. The Cellect patents were part of a larger family sharing a common priority date. Without PTA, all would have expired on the same day. But because several patents received substantial PTA (exceeding 700 days in some cases), their adjusted expiration dates extended well beyond a related patent in the family that received no PTA.

The PTAB found certain claims unpatentable for ODP, and the Federal Circuit affirmed. The court reasoned that the purpose of ODP is to prevent a patentee from obtaining a time-wise extension of protection for the same or an obvious variation of an invention. That purpose applies equally when the later expiration results from PTA rather than a later filing date.

The court distinguished prior decisions involving patent term extension (PTE) under 35 U.S.C. § 156, which held that ODP is based on the expiration date before PTE is added. The court emphasized that PTA and PTE are distinct statutory frameworks with different purposes: PTA compensates for delays in the prosecution of a particular patent, while PTE compensates for regulatory delays in bringing a product to market.

Why Cellect Matters

Before Cellect, many practitioners assumed PTA was "safe" from ODP — that it simply extended the patent's term as Congress intended and could not create a double patenting problem. Cellect eliminated that assumption. Now, any patent in a family that has more PTA than a related patent with patentably indistinct claims is potentially vulnerable to ODP.

This is particularly concerning for patent families where the parent application experienced significant prosecution delays while child applications moved through examination quickly. The parent ends up with substantial PTA; the children get little or none. Under Cellect, the parent's PTA-adjusted expiration creates ODP exposure unless the claims are patentably distinct.

Allergan (2024): The First-Filed, First-Issued Safe Harbor

In Allergan v. MSN Labs (Fed. Cir. 2024), the Federal Circuit clarified an important limitation on Cellect. The court held that a first-filed, first-issued, later-expiring claim cannot be invalidated via ODP by a later-filed, later-issued, earlier-expiring reference claim sharing a common priority date.

The court's reasoning was grounded in the purpose of the ODP doctrine itself. ODP exists to prevent a patentee from extending patent protection through a second patent. But when the allegedly offending patent was filed and issued first, and the reference patent was filed and issued later, the later patent does not extend the earlier patent's coverage — the later patent expires first. Requiring the parent to disclaim its PTA in this scenario would deny the patentee the term compensation Congress guaranteed under the American Inventors Protection Act (AIPA).

The court observed that this pattern is common and expected in patent prosecution: an applicant first seeks to protect the most valuable inventive asset, such as a pharmaceutical genus claim, and later files continuations on enhancements or specific compounds. The parent's prosecution is often more protracted, resulting in more PTA. The child applications proceed more efficiently and receive less PTA. The child patents expire no later than the parent, so there is no unjustified extension of protection.

The Allergan Safe Harbor in Practice

The Allergan safe harbor protects parent patents that meet three criteria:

1. First-filed — the parent application was filed before the reference application.
2. First-issued — the parent patent issued before the reference patent.
3. Later-expiring — the parent's PTA-adjusted expiration date is later than the reference patent's expiration date.

When all three conditions are met, the parent cannot be invalidated for ODP based on the later-filed, later-issued child, and the parent keeps its full PTA. This is significant relief for patent families following the typical prosecution pattern.

How Cellect and Allergan Work Together

The two decisions establish a framework:

Cellect rule: ODP analysis uses PTA-adjusted expiration dates. A patent with more PTA than a related patent with indistinct claims is potentially exposed to ODP.

Allergan exception: But if the patent with more PTA was also filed first and issued first, ODP does not apply to invalidate it based on the later-filed, later-issued, earlier-expiring reference.

Remaining risk: Patents that were filed later or issued later than their ODP reference — even if they have more PTA — remain subject to Cellect. And the Allergan safe harbor has not been tested in every configuration. For example, it is unclear how it applies when a patent is first-filed but not first-issued, or when the family tree is more complex than a simple parent-child relationship.

Worked Example: Evaluating ODP Risk in a Patent Family

When Allergan Does NOT Protect

The Allergan safe harbor does not apply in several important scenarios:

• Later-filed, later-issued patent with more PTA. If a continuation was filed later and issued later than the parent, but received more PTA due to extended prosecution delays, it is exposed to ODP under Cellect. The continuation would need a terminal disclaimer, which would cap its term to the parent's expiration and effectively eliminate the PTA advantage.
• Same filing date but different issuance order. The Allergan holding is specifically tied to first-filed and first-issued. If two applications share a filing date, issuance order alone may not be sufficient.
• Complex family trees. Families with multiple branches, cross-referenced terminal disclaimers, or interleaved filing and issuance dates require careful case-by-case analysis.

Strategic Implications for Prosecution

These decisions create several practical considerations for managing patent families:

Track PTA across the family. When prosecuting related applications, monitor PTA accrual in each application. Significant PTA differences between family members with similar claims create ODP risk under Cellect.

Be deliberate about filing and issuance order. The Allergan safe harbor is keyed to filing and issuance order. Where possible, ensure parent applications are allowed and issued before children with potentially indistinct claims.

Evaluate terminal disclaimers carefully. A terminal disclaimer filed proactively to avoid an ODP rejection will cap PTA. Before filing one, consider whether the Allergan safe harbor might apply, which would allow the patent to keep its PTA without a TD.

Consider claim differentiation. If family members can be drafted with patentably distinct claims, ODP may not apply regardless of PTA differences. This is the most reliable long-term strategy.

Monitor for further developments. A Petition for Certiorari was pending in Cellect at the time of the Allergan decision, and the law in this area continues to evolve.

Last reviewed: April 2026

Authorship: Written by the patentreply.ai editorial team. See our editorial methodology for how guides are drafted, sourced, and reviewed.

Legal disclaimer: This article is for informational purposes only and does not constitute legal advice. Consult a registered patent attorney or agent for advice specific to your situation. patentreply.ai is not a law firm.