Patent Protection for Future Embodiments: Key Lessons from the Federal Circuit’s Entresto Ruling

Patent Protection for Future Embodiments: Key Lessons from the Federal Circuit’s Entresto Ruling

On January 10, 2025, the Federal Circuit issued an important precedential decision regarding Novartis’s blockbuster heart failure drug Entresto (sacubitril/valsartan), providing key clarifications on written description and enablement requirements in patent law.^[1] The court reversed a district court’s finding that claims covering Entresto were invalid for lack of written description,^[2] while affirming the lower court’s determination that the claims were not proven invalid for lack of enablement or obviousness.^[3]

Entresto is an important asset for Novartis and is indicated for heart failure in both adult and pediatric patients.^[4] Last year, Novartis reports total sales of Entresto amounted to $7.822 billion.^[5] Entresto was Novartis’s top-selling drug in 2024, generating sales that exceeded their second-highest revenue generator, Cosentyx, by more than $1.5 billion.^[6]

Case Background

Novartis sued several generic manufacturers, including MSN pharmaceuticals, under the Hatch-Waxman Act after they sought FDA approval to market generic versions of Entresto.^[7] The case centered on U.S. Patent No. 8,101,659 (“the ‘659 patent”), which claims a pharmaceutical composition comprising the combination of valsartan (an angiotensin receptor blocker) and sacubitril (a neutral endopeptidase inhibitor) administered in a one-to-one ratio and in an effective amount to treat heart failure.^[8]

Importantly, Entresto is more than just a mixture of valsartan and sacubitril but rather includes these two active ingredients linked together in a single co-crystal complex, which was separately patented by Novartis in a later filed application.^[9] The original ‘659 patent does not actually show an exemplary pharmaceutical formulation comprising valsartan and sacubitril, but instead, the specific examples only present tablets or tablets containing valsartan as the sole active ingredient.^[10].

The co-crystal complex was first synthesized in January 2006, four years after the filing date of the ‘659 patent.^[11] As late as August 2005, Novartis’s scientists disputed if such a complex was even feasible.^[12] They conducted thousands of experiments including as many wild approaches as possible to synthesize the complex, eventually succeeding with one of these “out-of-the-box (irrational?)” methods.^[13]

MSN challenged the claims of the ‘659 patent on the grounds of indefiniteness, obviousness, enablement, and written description.^[14] This post focuses on the decisions the court made with regards to the challenges against enablement and written description. In U.S. Patent law, the written description requirement concerns whether the patent’s disclosure demonstrates that the inventor had possession of the invention at the time of filing. ^[15] The enablement requirement mandates that the disclosure must instruct a person with ordinary skill in the relevant field how to make and use the claimed invention without excessive experimentation.^[16]

The District Court’s Decision

Claim Construction

At the claim construction phase, the district court adopted the plain and ordinary meaning of “administered in combination,” rejecting MSN’s narrower interpretation that would have required administration as separate components (i.e. in a non-complexed form, such as a physical mixture).^[17] Like Ernesto, MSN’s generic product contained a complexed form of sacubitril and valsartan.^[18] Based on this construction, MSN stipulated to infringement but challenged the validity of the patent.^[19]

Enablement

The plaintiffs admitted that the ‘659 patent does not disclosure or suggest the complexed embodiment, seemingly permitting a discussion of enablement and written description.^[20] Consequently, the Defendants argued that the claims were invalid for not enabling the complex.^[21] The Plaintiffs assert that because the complex is an unknown, after-arising technology, enablement is not required for this embodiment of the invention.^[22]

The district court sided with the plaintiff, holding that “[e]nablement is judged as of the priority date, and later-existing state of the art may not be properly considered in the enablement analysis.”^[23] Abundant evidence indicates that a specific complex comprising the two pertinent actives a later-existing technology that need not be enabled because the co-crystal was unknown in 2002.^[24] The court also found that it is immaterial if such pharmaceutical complexes generally are the relevant technology because the Defendant also failed to show that they were known in the art in 2002.^[25]

Written Description

The district court held that the ‘659 patent claims lacked written description support because they covered valsartan-sacubitril complexes that were unknown at the time of filing.^[26] The written description requirement is meant to ensure that the inventor had possession of the claimed invention as of its filing date.^[27] In Chiron Corp. v. Genentech, Inc., the Federal Circuit court held that even though after-arising technology was outside the bounds of the enablement requirement, it cannot meet the written description requirement because the inventor could not have had possession of technology that did not exist at the time of filing.^[28] Relying on this precedent, the district court found the ‘659 patent invalid for lack of written description.^[29]

The Federal Circuit’s Analysis

Enablement

On enablement, the Federal Circuit affirmed the district court’s finding, reiterating that a specification need only enable the specific embodiments of the claimed invention known at the time of filing.^[30] Later-discovered technology, such as the specific valsartan-sacubitril complex used in Entresto, cannot be used to “reach back” and invalidate patent claims.^[31] This incentivizes innovation that improves upon the basic or underlying invention.^[32]

Written Description

The Federal Circuit’s reversal on written description hinged on a fundamental legal principle that the district court had overlooked. The court emphasized a critical distinction that lies at the heart of patent law: written description requirements apply specifically to what is claimed in the patent, not to all possible embodiments that might later infringe those claims.^[33] The Federal Circuit reversed on written description, emphasizing a crucial distinction: “The issue is not whether the ‘659 patent describes valsartan-sacubitril complexes. Because the ‘659 patent does not claim valsartan-sacubitril complexes, those complexes need not have been described.”^[34] This statement encapsulates a crucial boundary in patent law between the scope of patent claims and the scope of patent disclosure requirements.

The court explained that the ‘659 patent claims a pharmaceutical composition comprising valsartan and sacubitril “administered in combination.”^[35] The specification adequately supported this claim language by describing:

1. Pharmaceutical compositions comprising valsartan and a NEP inhibitor,^[36] wherein the NEP inhibitor is sacubitril;^[37]
2. Combination therapy with valsartan and a NEP inhibitor results in more effective anti-hypertensive therapy;^[38]
3. That “a therapeutically effective amount of each of the component[s] of the combination of the present invention may be administered simultaneously or sequentially in any order.”^[39]

These disclosures provided clear written description support for what was claimed at the time of filing: administering valsartan and sacubitril in combination.

The Federal Circuit emphasized the temporal aspect of this case. As previously mentioned, valsartan-sacubitril complex—the specific form used in Entresto—was not discovered until approximately four years after the priority date of the ‘659 patent. The court noted that “that complex… is not what is claimed” in the original patent.^[40] This timeline created a logical impossibility: the inventors could not have possessed or described something that did not exist at the time of filing. Yet the district court had effectively required them to do just that.

The Distinction Between Patentability and Infringement

Perhaps most significantly, the Federal Circuit criticized the district court for “erroneously conflat[ing] the distinct issues of patentability and infringement.”^[41] This confusion led the lower court astray in its written description analysis.

Claim interpretation must occur independently of infringement analysis.^[42] Judges must interpret patent claims based solely on their intrinsic merits, without any consideration of the allegedly infringing product.^[43] Only after this independent interpretation is complete should the court apply these construed claims to the accused device to determine whether infringement has occurred.^[44] This methodical approach prevents judicial bias from influencing claim interpretation and ensures that infringement determinations are based on objective analysis rather than subjective preferences. The fact that the claims were are written broadly enough to cover the complex form of Entresto does not retroactively change what needed to be described in the original patent.^[45]

Key Takeaways

1. Claim Scope vs. Infringement: The decision reinforces the distinction between what a patent claims (which must be described and enabled) and what might later infringe those claims. After-arising technology may infringe a patent even if that specific embodiment was not described in the original patent.^[46]

2. Temporal Context Matters: Written description must be evaluated based on what was known and claimed at the time of filing, not in light of later developments.^[47]
3. Claim Construction Independence: Claims must be construed based on their meaning at the time of invention, not based on whether they would cover later-developed technology.^[48]
4. “Possession” Test Clarification: The court indirectly clarified that “possession of the claimed subject matter” (the standard test for written description) refers to possession of what is expressly claimed, not all possible future embodiments that might fall within the claim scope.^[49]
5. Future Embodiments: The decision supports the principle that patent claims can cover future, unforeseen embodiments that still meet the claim limitations—even if those specific embodiments were not described in the original patent.^[50]

This analysis reinforces the longstanding principle that patent protection can extend to after-arising technology that falls within the scope of properly constructed claims. At the same time, it maintains the integrity of the written description requirement by focusing it on what was expressly claimed rather than expanding it to encompass all possible future implementations of the claimed invention. This decision provides valuable guidance for both patent owners and challengers, particularly in the pharmaceutical space where patents often cover basic inventions that may be implemented in various unforeseen forms as technology advances.

Outlook for Novartis

Despite this win for Novartis in early 2025, Novartis is inching towards a patent cliff with Entresto, with the ‘659 patent expiring on July 15, 2025.^[51] Even though Novartis will still hold key patents covering the amorphous and crystal forms of the API combination as well as the dosage regimen for chronic heart failure,^[52] generic versions of Entresto have been approved by the FDA and are expected to launch in mid-2025, sidestepping Novartis’s remaining patent coverage through labelling tweaks.^[53] Last month, Novartis announced a layoff of over 400 employees in New Jersey ahead of the expiration.^[54]

What are your thoughts on the Federal Circuit’s decision? Does it strike the right balance between rewarding innovation and allowing for technological advancement?