Enanta Pharmaceuticals Files Patent Infringement Suit Against Pfizer in European Union

Enanta Pharmaceuticals has filed a patent infringement lawsuit against Pfizer in the European Union over Pfizer's COVID-19 antiviral Paxlovid. The lawsuit alleges infringement on Enanta's European Patent No. EP 4 051 265, which covers coronavirus protease inhibitors. A hearing is expected within 12 months, with a decision and potential damages to follow. Enanta is a clinical-stage biotechnology company with a focus on discovering and developing small molecule drugs targeting viral infections and immune diseases.

Enanta Pharmaceuticals has filed a patent infringement lawsuit against Pfizer in the European Union, alleging infringement on Enanta's European Patent No. EP 4 051 265. The lawsuit, which was filed in the Unified Patent Court of the European Union, seeks a determination of liability for the use and infringement of the patent in the manufacture, use, and sale of Pfizer's COVID-19 antiviral, Paxlovid. The patent covers coronavirus protease inhibitors, a key component of Paxlovid.

Enanta, a clinical-stage biotechnology company focused on discovering and developing small molecule drugs targeting viral infections and immune diseases, believes that Pfizer designed Paxlovid via unlawful means. The company is seeking a determination of liability and potential damages for the infringement. The hearing is expected to occur within 12 months, with a decision and potential damages to follow.

Pfizer has responded to the lawsuit, stating that it is confident in its intellectual property (IP) surrounding Paxlovid and will respond in due course in court. The company has reported strong Q2 2025 results, with sales for Paxlovid growing 71% and the Covid-19 vaccine Comirnaty revenue surging 95%. However, the legal challenge posed by Enanta marks the second issue Pfizer has had to firefight this week, following a Phase III trial failure for a sickle cell disease candidate.

Enanta's US lawsuit against Pfizer, which was filed in June 2022, also claimed patent infringement. However, in December 2024, a federal judge in Massachusetts sided with Pfizer, granting that the US patent is invalid. Enanta has confirmed that it will appeal the decision, adding that it believes strongly in the merits of its case.

The lawsuit filed in the EU targets Pfizer's commercial activity in the 18 countries of the European Union. The company confirmed that the EP 4 051 265 patent is the European counterpart of the US patent number 11,358,953 that is the center of the US lawsuit.

Enanta Pharmaceuticals has a history of co-developing drugs with major pharmaceutical companies, including AbbVie for hepatitis C virus treatment glecaprevir/pibrentasvir. The company's focus on viral infections and immune diseases aligns with the current global health landscape and its potential impact on public health.

References:
[1] https://finance.yahoo.com/news/pfizer-battles-another-paxlovid-lawsuit-165337183.html
[2] https://www.ainvest.com/news/enanta-pharmaceuticals-files-patent-infringement-lawsuit-pfizer-european-union-court-2508/
[3] https://www.pharmaceutical-technology.com/news/pfizer-battles-another-paxlovid-lawsuit-from-enanta/