Back in July we wrote about the doctrine of equivalents (DOE) in bio/pharma cases in general, and the on-going saga of DOE in Lilly’s ALIMTA® litigation specifically. Last week, the Federal Circuit penned a new chapter, issuing a non-precedential decision in Eli Lilly and Company v. Apotex, Inc.

Didn’t this all end last June? Not quite.

At issue again is Lilly’s U.S. Patent No. 7,772,209 (“the ’209 patent”) claiming an “improved method” for treating patients by administering pemetrexed disodium in combination with folic acid and vitamin B12. As originally filed, however, the independent claims recited an “antifoliate,” not pemetrexed disodium (itself a species of antifolate). To overcome a prior art rejection during prosecution, Lilly narrowed that claim from administering an “antifoliate” to administering “pemetrexed disodium.”

The Federal Circuit in Hospira held that that amendment was tangential, DOE applied, and the alternative salt forms developed by Hospira and Dr. Reddy’s Laboratories (“DRL”) infringed.

Like Hospira and DRL, Apotex developed a different salt: here pemetrexed dipotassium. And as before, Lilly filed suit asserting DOE.

But here’s the wrinkle. As originally filed, claim 9, for example, recited a “method of any of claims 1-8 wherein the antifoliate is ALIMTA.” The Examiner rejected claims referencing “ALIMTA” as indefinite. Later, when Lilly filed the application that ultimately issued as the ’209 patent, it filed a preliminary amendment canceling the “ALIMTA” claims and prosecuting only the “pemetrexed disodium” claims. Thus, at issue here was whether the amendment replacing “ALIMTA” with “pemetrexed disodium” gave rise to prosecution history estoppel and whether any of the exceptions applied.

Apotex argued that the amendment was a narrowing one because “ALIMTA” is a broader term, referring to either pemetrexed alone or pemetrexed disodium specifically. The district court and Federal Circuit disagreed, concluding that the specification and prosecution history make clear that “ALIMTA” and “pemetrexed disodium” are synonymous and it was not a narrowing amendment. Accordingly, the Federal Circuit affirmed the district court’s grant of summary judgment.

The decision here clearly depended on the facts. But the Federal Circuit’s willingness to apply DOE in life science cases is evident. With the seeming uptick of DOE in life sciences, this case is, at a minimum, another reminder that life science patent practitioners need to keep the doctrine on their minds when engaged in prosecution, due diligence, and freedom-to-operate analyses.