TAKEAWAY: The context of claim amendments and arguments made during prosecution may affect equivalents encompassed within the scope of a patent’s claims.

The Federal Circuit recently upheld a district court’s finding in Eli Lilly & Co. v. Hospira, Inc. and Eli Lilly & Co. v. Dr. Reddy’s Laboratories, Ltd. that Hospira and Dr. Reddy’s Laboratories infringed Eli Lilly’s patents directed to methods of treatment with pemetrexed disodium under the doctrine of equivalents.

Eli Lilly obtained claims directed to a method for administering pemetrexed disodium, an antifolate, to a patient in need of chemotherapeutic treatment, including administering specific amounts of folic acid and vitamin B12 prior to the administration of pemetrexed disodium. During prosecution, Eli Lilly sought claims directed to a method for administering an antifolate to a patient in need of chemotherapeutic treatment. These broad claims were rejected as anticipated or as obvious over several of references. The anticipating reference disclosed treatment of mice using, among other substances, the antifolate methotrexate. The patent owner amended the claims to narrow “antifolate” to “pemetrexed disodium”, based on a dependent claim, and argued that none of the references taught using vitamin B12 to reduce toxicities associated with an antifolate. The claims were allowed and the application issued as U.S. Patent No. 7,053,065. Eli Lilly subsequently sued Dr. Reddy’s Laboratories and Hospira for infringement of the ’065 patent.

In an ANDA submission, Hospira and Dr. Reddy’s each sought approval by the FDA of treatment of a patient in need of chemotherapeutic treatment using a different antifolate, ditromethamine salt. Notably, while not reviewed in this discussion, the district court’s holding that Hospira literally infringed claims of the ’065 patent were overturned by the Federal Circuit. Thus, infringement of the claims by Hospira and Dr. Reddy’s rested on a theory of infringement under the doctrine of equivalents.

The Federal Circuit acknowledged that application of the doctrine of equivalents had several limitations, including (1) prosecution history estoppel; (2) vitiation of a particular claim element; (3) substantial differences from the claimed invention; (4) subject matter disclosed but not claimed; and (5) the equivalence cannot encompass the prior art. While prosecution history estoppel is presumed to attach to narrowing amendments, the presumption may be overcome if the amendment bears no more than a tangential relation to the equivalent in question.

In reaching its decision, the Federal Circuit determined that the amendment during prosecution was made to more clearly define Eli Lilly’s invention on methods of administering pemetrexed, and to avoid the anticipatory reference, which disclosed methods of administering methotrexate. The Federal Circuit reasoned that the amendment was merely tangential to the type of salt to which pemetrexed was complexed, and the prosecution history was clear that the amendment was intended to cover methods of administering other pemetrexed salts.

This case is a reminder that prosecution history estoppel requires more than a cursory review of claim amendments; the context of the amendments and arguments also matters. Further, when prosecuting claims, an applicant should carefully consider the reasons provided for narrowing amendments, as those reasons are likely to affect equivalents encompassed within the scope of the claims.