Enanta Pharmaceuticals Sues Pfizer Over Paxlovid Patent Infringement in EU.

Enanta Pharmaceuticals has filed a patent infringement suit against Pfizer in the Unified Patent Court of the European Union, seeking liability for use and infringement of European Patent No. EP 4 051 265 in the manufacture, use, and sale of Pfizer's COVID-19 antiviral, Paxlovid. The suit targets Pfizer's activities in the 18 countries of the European Union that are currently part of the UPC. Enanta Pharmaceuticals is a clinical-stage biotechnology company dedicated to creating novel small molecule drugs for viral infections and immunological diseases.

Enanta Pharmaceuticals, Inc. (NASDAQ: ENTA), a clinical-stage biotechnology company, has filed a patent infringement suit against Pfizer Inc. in the Unified Patent Court (UPC) of the European Union. The suit, filed on August 20, 2025, seeks a determination of liability for the use and infringement of European Patent No. EP 4 051 265 (the '265 Patent) in the manufacture, use, and sale of Pfizer's COVID-19 antiviral, Paxlovid™ (nirmatrelvir tablets; ritonavir tablets) [2].

The '265 Patent, granted to Enanta by the European Patent Office, covers coronavirus protease inhibitors and was granted based on a July 2020 patent application describing such inhibitors invented by Enanta scientists [1]. The enforcement action targets Pfizer's activities in the 18 EU countries currently participating in the UPC [2].

Under UPC procedures, a hearing on the infringement action is expected to occur within the UPC's published 12-month target, with a decision anticipated within weeks thereafter. If the UPC determines infringement occurred, subsequent proceedings would be required to determine damages [2].

This European legal action parallels ongoing U.S. litigation between the companies involving U.S. Patent No. 11,358,953, which is the American counterpart to the European patent [1]. Enanta's patent is based on a July 2020 application describing coronavirus protease inhibitors invented by the company's scientists [1].

Enanta Pharmaceuticals is dedicated to creating novel, small molecule drugs for viral infections and immunological diseases. The company's clinical programs are focused on respiratory syncytial virus (RSV) and its earlier-stage immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, including KIT and STAT6 inhibition [3].

References:
[1] https://www.investing.com/news/company-news/enanta-files-patent-infringement-suit-against-pfizer-over-paxlovid-93CH-4201876
[2] https://www.morningstar.com/news/business-wire/20250820282912/enanta-pharmaceuticals-files-patent-infringement-suit-against-pfizer-in-the-unified-patent-court-of-the-european-union
[3] https://www.marketscreener.com/news/enanta-pharmaceuticals-files-patent-infringement-suit-against-pfizer-in-the-unified-patent-court-of-ce7c51d2dd8df22c