On March 27, 2023, the U.S. Supreme Court heard oral arguments in Amgen Inc. v. Sanofi, a closely watched case on the issue of enablement under 35 U.S.C. § 112(a). Though not the main point of contention, the doctrine of equivalents (DOE) was brought up several times during oral arguments as an avenue to capture additional claim scope. Prior to the oral arguments, legal scholars had proposed, at least in the antibody context, to marry means-plus-function claim drafting to DOE as an approach to potentially salvage genus claims. This article provides some insights on the use of DOE in life sciences cases.
DOE is a long-standing doctrine judicially created to protect patent owners from alleged infringers who may circumvent the literal scope of a patent claim by making “unimportant and insubstantial” modifications to a patented invention. Over the decades since the doctrine was first established, courts have imposed major limitations on DOE to strike a balance between the inventor’s interest and public interest. One such limitation is prosecution history estoppel, which bars a patentee from recapturing through DOE subject matters surrendered during prosecution. However, in 2019, the Federal Circuit affirmed a finding of infringement under DOE in Eli Lilly & Co. v. Hospira, Inc., in spite of a narrowing amendment made during prosecution of Eli Lilly’s patent related to Alimta® for treatment of certain types of cancer with antifolates. The equivalents at issue were two pemetrexed salt forms, pemetrexed disodium and pemetrexed ditromethamine. An amendment from “an antifolate” to “pemetrexed disodium” was presented by Eli Lilly during prosecution in response to a prior art rejection. Finding that the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question, the Federal Circuit affirmed that prosecution history estoppel did not bar Eli Lilly’s infringement claim under DOE.
Following the guidance from the Federal Circuit, there has been an uptake on DOE related issues in the lower courts. For example, in 2020, the U.S. District Court for the District of Delaware addressed DOE in ViiV Healthcare Co. v. Gilead Sciences, where ViiV alleged that Gilead’s product for HIV treatment, bictegravir, infringed claim 6 of U.S. Patent No. 8,129,385 (the “’385 patent”). Claim 6 of the ’385 patent is directed to dolutegravir, an active pharmaceutical ingredient used in HIV treatments. Based on the structural differences between the difluoro benzyl ring in ViiV’s dolutegravir and the trifluoro benzyl ring in Gilead’s bictegravir, Gilead moved for summary judgment, arguing the two-fluorines limitation in claim 6 specifically excludes compounds with three fluorines. The court denied Gilead’s motion for summary judgment of non-infringement, finding that ViiV was not barred from asserting an infringement claim under DOE. To end the legal battle, Gilead and ViiV reached a US$1.25 billion global settlement and licensing agreement in 2022.
Given the recent attention on DOE, stakeholders should be aware that, even with its limitations, DOE can be a viable infringement theory in certain cases and should not be overlooked in strategic thinking on IP issues.
 Lemley, Mark A. and Sherko, Jacob S., The Antibody Patent Paradox (February 2023), The Yale Law Journal.
Eli Lilly and Co. v. Hospira, Inc., No. 18-2126 (Fed. Cir. 2019).
ViiV Healthcare Co. v. Gilead Scis., Inc., No. 18-224 (D. Del).