The Tangential Exception to Prosecution History Estoppel

| Daniel A. Kamkar


Before Lourie, Moore, and Taranto. Appeal from the District Court for the Southern District of Indiana.

Summary: A narrowing claim amendment does not necessarily surrender all equivalents of the claim element if the prosecution history shows that an equivalent is merely tangentially related to the amendment.

Eli Lilly brought two separate infringement suits under the Hatch-Waxman Act against Hospira and Dr. Reddy’s Laboratories (“DRL”) alleging that their New Drug Applications for a composition comprising pemetrexed ditromethamine infringes Eli Lilly’s patent. The patent at issue has claims directed to a method of chemotherapeutic treatment which requires administering “pemetrexed disodium.” In the parent application, Eli Lilly narrowed “antifolate” to “pemetrexed disodium” in response to a reference that disclosed the antifolate “methotrexate.” Following a bench trial on the claims against DRL, the district court found infringement under the doctrine of equivalents in that pemetrexed ditromethamine meets the pemetrexed disodium claim limitation. For the case against Hospira, the district court granted summary judgement of infringement under both literal infringement and the doctrine of equivalents.

In a combined appeal, the Federal Circuit reversed the district court’s finding of literal infringement against Hospira, but affirmed both findings of infringement under the doctrine of equivalents. The Federal Circuit found that it was clearly erroneous for the district court to hold that the step of administering pemetrexed disodium was literally infringed by pemetrexed ditromethamine, as they are different pemetrexed salts.

As for the doctrine of equivalents, the Federal Circuit found that the presumption of prosecution history estoppel, which attaches to narrowing amendments, was overcome because the patent’s prosecution history showed that the amendment from “antifolate” to “pemetrexed disodium” was made to distinguish pemetrexed from antifolates generally rather than to distinguish between pemetrexed salts. Furthermore, using different pemetrexed salts was merely a tangential change with no consequence for pemetrexed’s administration or mechanism of action within the body, and therefore were found to be equivalents.

Editor: Paul Stewart