Enanta Pharmaceuticals Sues Pfizer Over COVID-19 Drug Patent in EU: A Legal Dispute

Enanta Pharmaceuticals is suing Pfizer over a patent dispute related to COVID-19 drugs in the EU. Pfizer is a leading pharmaceutical company with a portfolio of products, including primary care, specialty care, oncology, and others, with the majority of sales coming from the US.

Enanta Pharmaceuticals, Inc. (NASDAQ: ENTA), a clinical-stage biotechnology company focused on creating novel small molecule drugs for viral infections and immunological diseases, has filed a patent infringement suit against Pfizer Inc. in the Unified Patent Court (UPC) of the European Union. The suit, filed under action number 35071/2025, 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).

The '265 Patent, granted by the European Patent Office, is based on Enanta's July 2020 patent application describing coronavirus protease inhibitors invented by Enanta scientists. This patent is the European counterpart of U.S. Patent No. 11,358,953 (the '953 Patent), which is involved in ongoing U.S. litigation between Enanta and Pfizer Inc. The infringement action targets Pfizer's activities in the 18 countries of the European Union that are presently participating in the UPC.

Under UPC procedures, a hearing on the infringement action is expected to occur within the UPC's published 12-month target, with the decision rendered within weeks thereafter. If the UPC determines there has been infringement, subsequent proceedings would be required to determine damages. All timelines remain subject to potential rights of appeal and other customary proceedings in European patent litigation.

Enanta Pharmaceuticals is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs, with a focus on indications in virology and immunology. The company's clinical programs are currently 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.

This action follows Enanta's recent patent grant for the '265 Patent and is part of its ongoing efforts to protect its intellectual property. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release, as actual outcomes and results may differ materially from what is expressed.

References:
[1] https://www.businesswire.com/news/home/20250820282912/en/Enanta-Pharmaceuticals-Files-Patent-Infringement-Suit-Against-Pfizer-in-the-Unified-Patent-Court-of-the-European-Union
[2] https://www.marketscreener.com/news/enanta-pharmaceuticals-files-patent-infringement-suit-against-pfizer-in-the-unified-patent-court-of-ce7c51d2dd8df22c