Enanta Pharmaceuticals, Inc. v. Pfizer Inc., Appeal No. 2025-1427 (Fed. Cir. Jun. 23, 2026)

CASE OF THE WEEK

Enanta Pharmaceuticals, Inc. v. Pfizer Inc., Appeal No. 2025-1427 (Fed. Cir. Jun. 23, 2026)

In our Case of the Week, the Federal Circuit affirmed summary judgment invalidating all claims of Enanta’s Patent No. 11,358,953 as anticipated by Pfizer’s public disclosure of nirmatrelvir, a key component of Pfizer’s “Paxlovid” COVID treatment drug.  The court held the ’953 patent was not entitled to the priority date of Enanta’s July 20, 2020 provisional application, and that without that priority, Pfizer’s April 6, 2021 public presentation of nirmatrelvir anticipated the asserted claims.  The ’953 patent claimed coronavirus protease inhibitor compounds defined by “Formula (VI-6a)” with “substituent” limits including “X = CN” and “A” as optionally substituted alkyl or heteroaryl.  The dispute centered on the definition of permissible substituents for “A,” specifically a –“NHC(O)-C1-alkyl” group found in Pfizer’s nirmatrelvir.  Enanta’s provisional application listed -NHC(O)-C2-C12-alkyl, while the later ’953 patent listed -NHC(O)-C1-C12-alkyl—i.e., a difference of one carbon atom.

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Editors:

Nika Aldrich, IP Litigation  Group Leader, Schwabe

Jason A. Wrubleski, Shareholder

Contributor:

Jason Evans, Associate