Enanta Pharmaceuticals, Inc.

Enanta Pharmaceuticals is escalating its patent battle over Pfizer’s Covid-19 antiviral Paxlovid. The Watertown, MA-based drugmaker announced Wednesday that it filed suit against Pfizer in the Unified Patent Court of the European Union. Enanta alleges that Paxlovid infringes its ‘265 patent based on a 2020 application that describes “coronavirus protease inhibitors invented by Enanta scientists.” Pfizer beat a similar challenge brought by Enanta in federal court in Massachusetts, but Enanta filed an appeal in February. In Europe, Enanta expects a hearing within the court’s 12-month target, and a decision “within weeks thereafter,” the company said in a news release. A Pfizer spokesperson told Endpoints News on Wednesday that the company is “confident in our IP surrounding Paxlovid and will respond in due course in court.” Pfizer’s BioNTech-partnered Covid vaccine has also been at the center of patent litigation, including an ongoing case in Massachusetts federal court brought by Moderna. Earlier this month , a UK appeals court upheld the validity of a key Moderna patent, marking a loss for Pfizer and BioNTech in the long-running legal fight among the three companies. At the time, Pfizer and BioNTech said they planned to appeal the UK ruling.

Paxlovid has risen to become to one of Pfizer’s best-selling drugs despite reduced demand for Covid-19-related treatment. Credit: Lady Jiff / Shutterstock.com. If you don’t succeed at first, try again – in separate regions. That’s the motto Enanta Pharmaceuticals is following, at least, after disclosing it has sued Pfizer in Europe over a patent infringement relating to Covid-19 treatment pill Paxlovid (nirmatrelvir/ritonavir). In June 2022, Enanta filed a lawsuit against Pfizer in a US district court in Massachusetts, claiming that the big pharma company infringed on a patent describing protease inhibitors invented by its scientists. Enanta has now followed that up with another filing in Europe, making the same accusation. Since being emergency authorised in 2021, anti-viral Paxlovid has generated Pfizer more than $26bn in global revenue. This includes a staggering $18.9bn in 2022 when Covid-19 cases were still prevalent. Despite waning demand for Covid-19 treatments, the pill still brought in $1.2bn in 2024, buoyed by government orders. However, Enanta – known for co-developing hepatitis C virus treatment glecaprevir/pibrentasvir with AbbVie – believes Pfizer designed Paxlovid via unlawful means. The US biotech stated it is “seeking a determination of liability for 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”. In an emailed statement to Pharmaceutical Technology, a Pfizer spokesperson said: “We are confident in our intellectual property (IP) surrounding Paxlovid and will respond in due course in court.” GlobalData Strategic Intelligence US Tariffs are shifting - will you react or anticipate? Don’t let policy changes catch you off guard. Stay proactive with real-time data and expert analysis. By GlobalData Learn more about Strategic Intelligence The lawsuit, filed in the European Union’s (EU) Unified Patent Court (UPC), targets Pfizer’s commercial activity in the 18 countries of the EU. The company confirmed the ’265 patent in question is the European counterpart of US patent number 11,358,953 (the ’953 Patent) that is the centre of the US lawsuit. Although it is technically ongoing, Enanta’s US lawsuit hit a major roadblock. In December 2024, a federal judge in Massachusetts sided with Pfizer, granting that the ‘953 patent is invalid. Enanta confirmed at the time it would appeal the decision, adding it “believes strongly in the merits of our case”. Pfizer reported strong Q2 2025 results this month, bucking a tepid earnings window that gripped the wider pharma industry. Sales for the Paxlovid grew 71% while the Covid-19 vaccine Comirnaty revenue surged 95%. However, the legal challenge posed by Enanta marks the second issue Pfizer has had to firefight this week. The big pharma company reported a Phase III trial failure for a sickle cell disease candidate purchased as part of a $5.4bn takeover of Global Blood Therapeutics in 2022. Pharmaceutical Technology Excellence Awards - The Benefits of Entering Gain the recognition you deserve! The Pharmaceutical Technology Excellence Awards celebrate innovation, leadership, and impact. By entering, you showcase your achievements, elevate your industry profile, and position yourself among top leaders driving pharmaceutical advancements. Don’t miss your chance to stand out—submit your entry today! Nominate Now

WATERTOWN, Mass.--(BUSINESS WIRE)--Aug. 20, 2025-- Enanta Pharmaceuticals, Inc. (NASDAQ: ENTA), a clinical-stage biotechnology company dedicated to creating novel, small molecule drugs for viral infections and immunological diseases, announced today that it has filed suit in the Unified Patent Court (UPC) of the European Union against Pfizer Inc. and certain of its subsidiaries (action number 35071/2025), seeking a determination of liability for 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). This enforcement action targets Pfizer’s activities in the 18 countries of the European Union that are presently participating in the UPC. The European Patent Office’s recent grant of the ‘265 Patent to Enanta was published in the European Patent Bulletin today. The ‘265 Patent is based on Enanta’s July 2020 patent application describing coronavirus protease inhibitors invented by Enanta scientists. The ‘265 Patent is the European counterpart of U.S. Patent No. 11,358,953 (the ’953 Patent) involved in ongoing U.S. litigation between Enanta and Pfizer Inc. 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. About Enanta Pharmaceuticals, Inc. Enanta 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 an emphasis on indications in virology and immunology. Enanta’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. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing hepatitis C virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® (U.S.) and MAVIRET® (ex-U.S.) (glecaprevir/pibrentasvir). A portion of Enanta’s royalties from HCV products developed under its collaboration with AbbVie contribute ongoing funding to Enanta’s operations. Please visit www.enanta.com for more information. Forward Looking Statements Disclaimer This press release contains forward-looking statements, including statements with respect to Enanta’s filing in the UPC of a suit against Pfizer Inc. and certain of its subsidiaries seeking a determination of liability for use and infringement of Enanta’s patent and Enanta’s expectations with respect to any further action with respect to such proceedings. Statements that are not historical facts are based on management’s current expectations, estimates, forecasts and projections about Enanta’s business and the industry in which it operates and management’s beliefs and assumptions. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors and risks that may affect actual results include: Enanta is competing to develop intellectual property in areas of small-molecule drug development that are highly competitive; issued patents, including those covering one or more of its product candidates, could be found invalid or unenforceable if challenged in court and could be costly to defend and be a distraction for Enanta’s senior management and scientific personnel; intellectual property litigation may lead to unfavorable publicity that harms Enanta’s reputation and causes the market price of its common stock to decline; and other risk factors described or referred to in “Risk Factors” in Enanta’s Form 10-K for the fiscal year ended September 30, 2024 and other periodic reports filed more recently with the Securities and Exchange Commission. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Enanta undertakes no obligation to update or revise these statements, except as may be required by law. View source version on businesswire.com: https://www.businesswire.com/news/home/20250820282912/en/ Media and Investor Contact Jennifer Viera 617-744-3848 jviera@enanta.com Source: Enanta Pharmaceuticals, Inc.