Section 112 Is the New OTDP — Has Biotech’s Least Favorite Thorn Been Upstaged?
Let’s pour one out for obviousness-type double patenting.
Earlier in my career I was “lucky” to immerse myself in obviousness-type double patenting law (known by the catchy term “OTDP”) in all of its unsavory flavors and bizarre footnotes—cases that turned every OTDP argument into Mr. Toad’s Wild Ride[1] at the Federal Circuit (looking at you, Lilly Prozac®, GSK Augmentin®, Pfizer Celebrex®, and Lilly Gemzar®)[2]. Mercifully, cases like Otsuka Abilify®[3] and Lilly Alimta®[4] steadied the ship, before Gilead Tamiflu[5] unleashed a whole world of time-wise extension angst.
But then the courts reminded everyone that, actually, § 112 never went anywhere. And with a string of decisions flattening ambitious biotech claims for lack of written description and enablement, § 112 has stepped into the role OTDP once played so reliably: the stealth assassin of high-value portfolios.
The Pivot: From Patent-Term Anxiety to Possession-and-Scope Reality
Biotech built its modern claim strategies during the golden age of platform claims and continuation practice, assiduously threading the OTDP needle with families upon families of related filings. OTDP anxiety might have peaked when the Federal Circuit started making noises in 2014’s Gilead Tamiflu case—and then finally confirmed in In re Cellect—that patent term adjustment isn’t a force field against OTDP, and that mismatched expiry dates can still be a problem you can’t always fix cleanly after the fact. The bar responded with still more careful claiming and disclaiming. Problem managed, more or less.
Then the courts re-centered the world around § 112. The Supreme Court, in a unanimous enablement decision, told everyone that claiming vast functional territory requires disclosures that actually enable the full scope, not an instruction to “try your way through the genus.”[6] And the Federal Circuit, for its part, has not been shy about saying “you didn’t possess that” when applicants stitched together broad biochemical claim language from generic building blocks and a handful of exemplars.[7] If OTDP made term planning annoying, § 112 now makes aggressive claim scope existential.
Seagen Inc. v. Daiichi Sankyo Company, Ltd.: The Latest Reminder That Written Description and Enablement Are Not Optional
In a recent, front-page-worthy antibody–drug conjugate (“ADC”) case[8], the Federal Circuit took a hard look at a continuation claim set aimed at a blockbuster therapy and asked the only question that matters under § 112(a): where, exactly, is the disclosure that shows you possessed what you’re claiming, and how does your specification teach others to make and use the full scope without a research project? The court’s answers were emphatic: not here, and it doesn’t.
The patent tried to reach a defined subgenus of peptide linkers within ADCs. The earliest filing described a sprawling genus of peptide possibilities (tens of millions of theoretical tetrapeptides, if you’re counting at home), but never actually marked the trail to the precise “Gly/Phe-only” tetrapeptide universe that later claims targeted. The inventors’ own testimony didn’t help: if in 2015 you first saw the specific linkers in the wild—when your competitor disclosed no less—possession in 2004 is a tough sell. As for enablement, the claim language swept in ADCs using any drug moiety so long as it’s intracellularly cleaved in a patient. Without a unifying principle to teach which combinations will work across that scope—and in an unpredictable art—the specification left skilled artisans to run assays until they struck gold. The Supreme Court has a word for that: trial-and-error discovery. That’s not enablement.
Verdict: written description and enablement failures, damages vacated, and the PTAB appeal dismissed as moot because, once § 112 knocks out your claims, everything else is academic.
Why This Stings More Than OTDP
OTDP was a planning problem. It demanded hygiene: family alignment, terminal disclaimers, and a realistic view of term. Annoying? Yes. Career-ending for a claim set? Often not. You could usually paper over OTDP with a signature and a shortened expiry.
Section 112 is different. It is substantive. No terminal disclaimer can cure a missing blaze mark, and no deft expert can enable a functional genus that your specification doesn’t actually teach. When § 112 lands, it doesn’t trim your term; it eliminates your claims and vacates your judgment.
Practical Takeaways (That You Already Know, But Now with Consequences)
Biotech claims that reach function first and structure later are in a post-112-enforcement world. Written description demands that you show you had the tree, not just that your forest included a million “possible” trees. Enablement demands that you teach others how to make and use the full breadth you claim, not that you’ve flagged a few exemplars and handed the rest to the screening team. Continuation practice is still essential, but it’s not a time machine. Priority only travels as far as your earliest disclosure actually goes.
So yes, OTDP remains a hazard, and no one is forgetting that portfolio-level risk. But in 2025, §112 is the doctrine doing the heavy lifting in biotech validity fights. If you’re feeling nostalgic for the days when your biggest worry explaining to the client why you had to trim some term, the Federal Circuit has a message: mull the OTDP one-way versus two-way tests to your heart’s content, but §112 is where the rubber hits the road now. And just in time for the Supreme Court to give serious thought into taking up In re Entresto.
The Bottom Line
Section 112 has decisively replaced OTDP as the primary litigation and PTAB vulnerability for ambitious biotech claims.
Courts are demanding concrete possession of subgenera and true enablement of functional breadth, not suggestive genus disclosures plus assays.
Claiming strategy must now be built around disclosure-first breadth: exemplify subgenera you care about, articulate unifying structural or mechanistic principles, and write specifications that actually teach across the scope you want to keep.
Grim? Maybe. But the fix is within the four corners of your spec. In the post-Amgen world, §112 is not just a box to check. It is the box.
If you have questions about this Client Alert or are interested in additional details or guidance, please reach out to Greg Chopskie (greg.chopskie@pierferd.com) or your regular PierFerd contact for assistance.
This publication and/or any linked publications herein do not constitute legal, accounting, or other professional advice or opinions on specific facts or matters and, accordingly, the author(s) and PierFerd assume no liability whatsoever in connection with its use. Pursuant to applicable rules of professional conduct, this publication may constitute Attorney Advertising. © 2025 Pierson Ferdinand LLP.
[1] Alas, younger members of the bar might not have ridden the legendary ride.
[2] Eli Lilly & Co. v. Barr Labs., Inc., 251 F.3d 955 (Fed. Cir. 2001); Geneva Pharms. v. GlaxoSmithKline, 349 F.3d 1373 (Fed. Cir. 2003); Pfizer, Inc. v. Teva Pharms. USA, Inc., 518 F.3d 1353 (Fed. Cir. 2008); Sun Pharm. Indus., Ltd. v. Eli Lilly & Co., 611 F.3d 1381 (Fed. Cir. 2010).
[3] Otsuka Pharm. Co., Ltd. v. Sandoz, Inc., 678 F.3d 1280 (Fed. Cir. 2012).
[4] Eli Lilly & Co. v. Teva Parenteral Meds., Inc., 689 F.3d 1368 (Fed. Cir. 2012).
[5] Gilead Sciences, Inc. v. Natco Pharma Ltd., 753 F.3d 1208 (Fed. Cir. 2014).
[6] Amgen Inc. v. Sanofi, 143 S. Ct. 1243 (2022).
[7] See, e.g, Juno Therapeutics, Inc. v. Kite Pharma, Inc., 10 F.4th 1330 (Fed. Cir. 2021).
[8] Seagen Inc. v. Daiichi Sankyo Company, Ltd, Case Nos. 23-2424 and 24-1878 (Ded Cir. Dec. 2, 2025).
