On January 10, 2025, the Federal Circuit issued a significant decision in In re Entresto (Sacubitril/Valsartan) Patent Litigation, reversing a district court ruling that had found claims of Novartis’ U.S. Patent 8,101,659 (“the ’659 patent”) invalid for lack of written description. The appellate court affirmed the district court’s rulings that the patent was not invalid for obviousness or lack of enablement, solidifying Novartis’ ability to protect its blockbuster drug, Entresto®.

This decision highlights several key patent law principles, particularly in the areas of written description, enablement, and obviousness. Here’s a breakdown of the major issues addressed by the court.

1. Written Description – The Core Issue on Appeal

The Federal Circuit reversed the district court’s finding that the ’659 patent lacked an adequate written description. The lower court had ruled that because the patent did not describe a valsartan-sacubitril complex, it failed the written description requirement. However, the Federal Circuit clarified that the claims did not specifically require such a complex—they covered valsartan and sacubitril administered in combination, not in a bound form.

Key Takeaway:

A patent’s written description must support what is actually claimed, not an unclaimed feature of the accused product. The court found that the patent sufficiently described the claimed combination therapy, even though it did not describe the later-developed valsartan-sacubitril complex.

2. Enablement – The Patent Need Only Enable the Claimed Invention

The district court had found that the ’659 patent enabled the claimed invention, and the Federal Circuit affirmed this conclusion. The court held that because valsartan-sacubitril complexes were unknown at the time of filing, Novartis was not required to enable them in its patent.

Key Takeaway:

Later-developed technologies cannot be used to argue that an earlier patent lacks enablement. If the claimed invention was enabled based on the state of the art at the time of filing, the patent remains valid.

3. Obviousness – No Clear Motivation to Combine

The court also upheld the district court’s ruling that the asserted claims were not obvious. The defendants (generic pharmaceutical manufacturers) argued that a person of ordinary skill in the art would have been motivated to combine an ARB (valsartan) and an NEP inhibitor (sacubitril) based on prior studies of similar drug combinations.

However, the court found:

• The prior art did not directly suggest combining valsartan with sacubitril.
• Sacubitril was one of over 100 known NEP inhibitors in 2002, and it had never been tested in humans or animals for hypertension or heart failure.
• The available studies on other NEP inhibitors showed discouraging results.

Key Takeaway:

Obviousness cannot be based on hindsight—just because an invention later proves effective does not mean it was obvious at the time of the patent filing.

Conclusion: A Win for Novartis and Strong Patent Protection

This decision strengthens Novartis’ patent protection for Entresto®, a drug with annual U.S. sales exceeding $3 billion. It reinforces the principle that:

1. The written description requirement applies to what is actually claimed, not later-developed variants of the product.
2. Enablement is judged based on what was known at the time of filing, not what was developed later.
3. Obviousness must be based on clear motivation and reasonable expectation of success from the prior art.

For pharmaceutical innovators, this case underscores the importance of careful patent drafting and robust litigation strategies. Meanwhile, for generic manufacturers, it highlights the challenges of proving invalidity when prior art does not clearly suggest the patented invention.

By Charles Gideon Korrell