According to the lawsuit, Sanofi has failed to provide partner Regeneron adequate information regarding the sales of Dupixent—including agreements with payers and pharmacy benefit managers that determine pricing and rebates for the drug.
Regeneron revealed in its annual SEC report on Wednesday that it has sued Sanofi, claiming that its Dupixent partner “breached certain provisions” of their agreement around the blockbuster anti-inflammatory drug.
Regeneron claimed in its lawsuit that Sanofi had failed to provide it “full access to material information” regarding Dupixent sales, especially contracts between Sanofi and pharmacy benefit managers and other payers, which include the discounts and rebates that establish the final pricing of Dupixent.
“Because Regeneron and Defendants split Dupixent’s profits in the United States, Regeneron effectively pays for half of these rebates and discounts,” the suit read. “In violation of the Collaboration Agreement, Defendants have stonewalled Regeneron’s repeated requests for full access to the PBM Agreements.”
Additionally, Regeneron claimed that Sanofi has blocked its attempts to “fully audit their books and records related to Dupixent.” Even without access to the PBM Agreements, Regeneron’s independent audit “identified a significant monetary adjustment, many multiples of $75,000, that Defendants owed Regeneron in connection with commercializing Dupixent.” The pharma suggests that it could unearth “even larger errors” when given access to Sanofi’s records.
Regeneron filed its complaint in November last year with an amendment made a month later. The pharma is seeking declaratory judgement, injunctive relief and damages.
“We are in full compliance with the terms of our collaboration agreement with Regeneron,” a Sanofi spokesperson said in a statement emailed to BioSpace. “We remain focused on our shared priority with Regeneron - ensuring we continue to support the community of patients and caregivers who rely on Dupixent to treat their immunological conditions. We will not otherwise comment on the litigation.”
Dupixent is a powerhouse pharma asset, indicated for atopic dermatitis, asthma, chronic rhinosinusitis with nasal polyps, eosinophilic esophagitis and, most recently, chronic obstructive pulmonary disease. The biologic, a humanized IgG4 monoclonal antibody, works by blocking IL-4 and IL-13 signaling, thus dampening the inflammatory response.
Dupixent is a critical asset for Regeneron. In 2024, the drug emerged as its top-selling product, with more than $14.1 billion in sales, a 22% increase from the year prior. Dupixent beat out other heavy hitters, including the cancer therapy Libtayo and the blockbuster eye franchise Eylea. In 2025, the company is awaiting further regulatory decisions for Dupixent, including for chronic spontaneous urticaria and bullous pemphigoid.
Sanofi and Regeneron’s Dupixent partnership started in 2007, when the French pharma paid $85 million upfront and promised up to $475 million in research funding disbursed in the five years following the contract. In exchange, Sanofi gained the right to co-develop several of Regeneron’s assets, including the candidate that would become Dupixent.
Update (February 7): This story has been updated to include a statement from Sanofi.
