Enanta lawsuit claims Pfizer's Paxlovid infringes its patent

US biotech Enanta Pharma has filed a lawsuit against Pfizer, claiming that its oral antiviral for COVID-19 Paxlovid infringes one of its patents and seeking damages from the pharma giant.

The suit – filed in a Massachusetts district court – claims that Paxlovid (nirmatrelvir and ritonavir) infringes its 11,358,953 patent which covers "compounds and pharmaceutically acceptable salts which inhibit coronavirus replication activity, and methods of treating a coronavirus infection" and was awarded earlier this month.

If the complaint is upheld, Enanta could be in line for a share of Pfizer's revenues from Paxlovid, expected to make a colossal $22 billion in sales this year, after launching in December 2021.

Enanta has a long heritage in the development of antiviral compounds, working with AbbVie on therapies for hepatitis C virus (HCV) infection including Viekira Pak (paritaprevir/ritonavir/ombitasvir/dasabuvir) and Mavyret/Maviret (glecaprevir/pibrentasvir).

It is also developing its own therapies for respiratory syncytial virus (RSV), human metapneumovirus (hMPV) and chronic hepatitis B virus (HBV), and started work on COVID-19 early in in the pandemic focusing on 3CL protease – the same target as nirmatrelvir.

It has since advanced a lead candidate (EDP-235) into phase 1 clinical testing and claimed a fast-track designation for the drug from the FDA, according to court documents.

Enanta's suit is asking for a judgment that Pfizer has infringed the '953 patent plus damages to compensate for that infringement and costs, with any award trebled because it claims the big pharma has done so wilfully.

The company said it "recognises the importance of Paxlovid's availability to patients and does not intend to seek an injunction or take other action in this litigation that would impede the production, sale or distribution of Paxlovid."

However, it "seeks fair compensation for Pfizer's use of a coronavirus 3CL protease inhibitor claimed in the '953 patent."

There's a potential third wheel in the dispute, according to SVB Securities analyst Rosanna Ruiz, who said in a research note that Pardes Biosciences filed a patent on its 3CL protease inhibitor PBI-0451 earlier than Enanta, according to an Investors Business Daily report.

The legal challenge carries a risk as well, as it could cupper the development of Enanta's drug – and possibly Pardes' – if Pfizer can prove it was the first to develop a drug candidate targeting the protease. Either way, the legal wrangling is likely to take years to be resolved.