Obviousness-type double patenting and terminal disclaimers

Double patenting stops one owner from holding two patents on the same invention, or on obvious variants of it. Statutory double patenting (claims of the same scope) rests on 35 U.S.C. § 101 and cannot be cured by a terminal disclaimer. Obviousness-type, or nonstatutory, double patenting is judicially created and can be: the owner gives up any term that would run past the reference patent's term and agrees that the patent is enforceable only while it and the reference patent are commonly owned. For anyone asserting, buying or licensing a patent family, those conditions decide what each patent is worth.

Two kinds of double patenting

Statutory double patenting applies when two patents claim the same invention, meaning claims of identical scope. It rests on 35 U.S.C. § 101, read as allowing one patent for an invention, not two. A terminal disclaimer cannot overcome it; one of the conflicting claims has to be cancelled or changed so the scopes differ.

Nonstatutory, or obviousness-type, double patenting (ODP) applies when the claims are not identical but are not patentably distinct: the claim under examination is anticipated by, or would have been obvious over, a claim of the reference patent. The comparison is claim against claim. The reference patent's specification is used to understand its claims, not treated as prior art, which is why ODP can apply between patents that are not prior art to each other at all. ODP is judicially created and can be overcome by a terminal disclaimer. The USPTO's guidance on both kinds is in MPEP 804.

The obviousness half of the analysis follows the familiar logic of § 103, with the reference patent's claims standing in for the prior art; anticipation vs. obviousness covers that reasoning.

Why the doctrine exists

MPEP 804 gives two reasons. The first is term: without the doctrine, an owner could obtain later patents on obvious variants of an invention and stretch exclusivity past the term of the first patent. The second is multiple owners: if patents on obvious variants of one invention ended up with different companies, an accused party could be sued separately by each of them for what is in substance the same invention.

The terminal disclaimer answers both concerns, and its two conditions map onto them.

What a terminal disclaimer costs

A terminal disclaimer filed to overcome ODP does two things:

1. It ties the term. The owner disclaims the part of the patent's term that would extend beyond the term of the reference patent.
2. It ties ownership. Under 37 C.F.R. § 1.321(c), the disclaimer must include a provision that the patent will be enforceable only for and during the period that it and the reference patent are commonly owned.

The second condition is the one that bites in transactions. If a seller splits a family and sells the disclaimed patent without its reference patent, the disclaimed patent becomes unenforceable for as long as the two are owned separately. A buyer who wants enforceable rights usually needs every patent linked by terminal disclaimers, not only the one that reads on the target product.

The § 121 safe harbor for divisionals

When the USPTO issues a restriction requirement and the applicant files a divisional application for the restricted-out claims, 35 U.S.C. § 121 protects that divisional: a patent issuing on an application filed as a result of a restriction requirement cannot be used as a reference against the original application or patent, or the reverse. Divisionals filed this way usually need no terminal disclaimer against the parent.

The protection follows the restriction requirement, so practitioners check the basis rather than the label. They confirm that a restriction requirement was actually made in the parent's file, that the later application was filed as a result of it, and that its claims stayed within the group the restriction separated out. A continuation filed instead of a divisional, or claims that drifted across the restriction line, may leave the patent outside the safe harbor.

Patent term adjustment and the Cellect problem

Family members often share the same 20-year base term, because a continuation's term runs from the earliest US non-provisional filing date it claims. They still expire on different days, because patent term adjustment (PTA) under 35 U.S.C. § 154(b) is calculated for each patent separately, based on delays in its own prosecution.

In In re Cellect, LLC, 81 F.4th 1216 (Fed. Cir. 2023), the Federal Circuit held that ODP is assessed using the patents' expiration dates after PTA. A patent extended by PTA beyond an earlier-expiring, patentably indistinct reference patent can therefore be invalid for ODP, not merely shortened, if no terminal disclaimer ties the two together.

Two related decisions define the edges:

• Gilead Sciences, Inc. v. Natco Pharma Ltd., 753 F.3d 1208 (Fed. Cir. 2014): a later-issued patent that expires earlier can serve as the double-patenting reference. Issue order does not protect the earlier-issued patent; expiry dates drive the analysis.
• Novartis AG v. Ezra Ventures LLC, 909 F.3d 1367 (Fed. Cir. 2018): ODP does not invalidate a validly obtained patent term extension under 35 U.S.C. § 156. Term added by PTA and term added by a § 156 extension are treated differently.

A hypothetical family

Take two hypothetical patents owned by one company:

• Patent A is the parent, filed 1 March 2014. It has no PTA and expires 1 March 2034.
• Patent B is a continuation of A. Its claims add one well-known feature to A's claim 1. B carries 300 days of PTA, so it would run until late December 2034. No terminal disclaimer was filed, because the examiner never raised ODP.

Under Cellect, if B's claims are not patentably distinct from A's, B's extra ten months rest on an obvious variant of an invention whose protection ends in March 2034. B's claims are exposed to an ODP invalidity challenge. Reverse the issue dates and the analysis is the same: under Gilead, A can serve as the reference because it expires first. Had a terminal disclaimer been filed during prosecution, B would expire with A and be enforceable only while the two stay in common ownership.

Expiry dates are central to this analysis; when does a US patent expire explains how to work them out, including PTA.

What to check before asserting or buying

1. Map the family. List every US member and how it relates to the others: continuation, divisional or continuation-in-part. Patent families explained covers how to read those relationships.
2. Compute each expiry date with PTA and any § 156 extension, from the patent and its file history rather than an estimate from the filing date.
3. Find every terminal disclaimer. Read each file wrapper, note which reference patents each disclaimer names, and draw the resulting groups.
4. Confirm common ownership across each disclaimer-linked group, today and for the period you care about, using the recorded assignments. In a purchase, scope the deal around whole groups.
5. Flag Cellect exposure. Look for members whose PTA carries them past a related member with similar claims and no terminal disclaimer between them, then compare the claims.
6. Check divisional status. For any member relying on § 121, confirm the restriction requirement, the divisional filing and that its claims stayed within the restricted group.
7. Check for identical claims. Statutory double patenting is rare, but where it exists no disclaimer helps.

Whether and how a gap you find can still be addressed is a question for counsel. The checklist is about knowing the gap exists before a licensee, an accused infringer or a buyer's counsel finds it.

Where One Transform fits

One Transform's Validity search examines a patent the way an opposing party would. It builds a prior-art record and analyzes anticipation (§ 102), obviousness (§ 103), definiteness and enablement (§ 112), eligibility (§ 101), prosecution history and double-patenting exposure. It scores the patent claim by claim on a 0–10 scale and cites the references and reasoning behind each conclusion. When you are screening several portfolios, the Acquisition Targets search ranks patents and portfolios by fit to a goal you define, and the shortlist can then go through Validity one patent at a time.

Next step

Before your next assertion or acquisition, list the terminal disclaimers in the family and confirm who owns each linked patent. To check the double-patenting exposure claim by claim, start a Validity search from the One Transform product overview.

This article is general information about patent practice, not legal advice. For advice on a specific matter, consult a registered patent attorney or agent.