Guest post by Professors Jonathan S. Masur (Chicago Law) and Lisa Larrimore Ouellette (Stanford Law).
This blog recently covered the Federal Circuit’s important decision in In re Entresto (Novartis Pharmaceuticals v. Torrent Pharma), 125 F.4th 1090 (Fed. Cir. 2025), which upheld patent claims even though they covered after-arising technology that was not described or enabled in the specification. As Dennis noted, the Federal Circuit appeared to depart from well-established prior law on the subject. But as we explain in our forthcoming article, Disclosure Puzzles in Patent Law, we believe the court should move the law further still from where it stands—and it should correct some of its reasoning along the way.
To review, In re Entresto involved a patent that claimed a pharmaceutical composition of two hypertension drugs, valsartan and sacubitril, “in combination.” When the patent was filed, the only known method of combining these chemicals was in a physical mixture. That is the only combination method disclosed in the specification. In the intervening years, however, scientists have discovered a means of combining the two chemicals in a “complex,” an arrangement in which they are connected by weak chemical bonds. This is the method used to make the accused infringing drug. The patent owner argued successfully that the claim language (“in combination”) was broad enough to cover this mode of combination. But the fact that the use of a complex was after-arising technology—and thus the specification said nothing about it—raised written description and enablement issues.
The Federal Circuit upheld the patent against both challenges for basically the same reason: that the specification demonstrated that the patentee possessed and enabled the full scope of the claims at the time the patent application was filed. In other words, the patent claimed the two chemicals “in combination,” and the specification had indeed described and enabled the two chemicals “in combination.” But the court’s reasoning was peculiar. The court asserted that the after-arising technology—the combination of the two chemicals into a complex—“is not what is claimed.” To argue otherwise, the Federal Circuit declared, would be to “erroneously conflate[] the distinct issues of patentability and infringement.”
It is hard, however, to see how this could be right. The parties stipulated that the version of this invention made with a complex infringed the claims. That necessarily meant that the version of the invention using a complex was within the scope of the claims—that it was encompassed by the language “in combination.” If that is the case, then in what sense is the version made with the complex not claimed by the patentee?
On written description, the Federal Circuit nonetheless arrived at the right answer, though for misguided reasons. As Dennis noted, Entresto appears to conflict with the Federal Circuit’s prior decision in Chiron v. Genentech, 363 F.3d 1247 (Fed. Cir. 2004). But we think this is a good thing. As we explain in our article, after-arising technology is not the type of problem that the written description doctrine was developed to police. Written description exists to deal with a particular type of problem: patentees who write claims that would capture embodiments of the invention that could be made at the time of filing, but that the patentee did not actually invent. If Chiron’s reasoning were taken seriously, it would essentially always invalidate claims that capture after-arising technology. Otherwise-valid patents could be invalidated due to technological developments that the patent drafters could not have foreseen. Clarifying that written description shouldn’t be used to invalidate claims that cover after-arising technology is a step in the right direction.
Enablement is more complicated, and here we think the Federal Circuit failed to identify the right questions. The seminal case is In re Hogan, 559 F.2d 595 (C.C.P.A. 1977), under which it is irrelevant whether a specification enables after-arising technology. As we explain in our article, we agree with Hogan that if a claim is fully enabled at the time of filing, then it should be enabled forever.
However, completely ignoring the enablement of after-arising technology violates the principle that the scope of a patent should be commensurate with its disclosure. Thus, as a matter of infringement, the claim should capture after-arising technology only if a PHOSITA with access to the specification plus the new technology could implement the embodiment with that new technology. If it would take undue experimentation to figure out how to implement it, then the claim shouldn’t reach the nonenabled after-arising variant. Reading a claim to cover after-arising technology that is not enabled by the patent specification plus the new technology itself would give the patentee a property right over a version of the invention that she has not taught anyone to make or use.
Our article suggests multiple doctrinal routes by which courts could reach this enablement result, including claim construction, the reverse doctrine of equivalents (for literal infringement), or a broadened ensnarement doctrine (for infringement by equivalents). In re Entresto hints at one doctrinal resolution of this issue by stating that “valsartan-sacubitril complexes … include the claimed invention along with additional unclaimed features.” If the use of a “complex” is an “unclaimed element,” then it is blackletter law that this element need not be enabled or described.
Alternatively—and perhaps more consistently with the district court’s claim construction—the after-arising “complex” method is one variant of the explicitly claimed “in combination” element. In that case, the relevant question is whether combining valsartan and sacubitril in a complex involved a simple and predictable application of the “complex” method to this context (in which case the courts were right to find this claim valid and infringed), or whether this involved additional extensive experimentation (in which case the claim should be non-infringed). The patent owner’s argument that it later patented the “nonobvious discovery of valsartan and sacubitril in the form of a complex” suggests there may be evidence for the latter—but we don’t know because this wasn’t a question the courts asked. The important point is that rather ignoring enablement issues for after-arising variants of an invention, courts should consider whether patentees are seeking scope disproportionate to what they invented and disclosed.
As we suggested in Disclosure Puzzles in Patent Law, the modern enablement and written description doctrines give rise to a great number of conceptual puzzles, particularly when they interact with after-arising technology. Entresto is evidence of both the puzzles’ complexity and their importance. It is also evidence that the Federal Circuit has made some progress in thinking through these puzzles, but that more remains to be done.