New Life for Doctrine of Equivalents

Author:Mr Paul Devinsky
Profession:McDermott Will & Emery

Co-authored by Ms Natalia Blinkova

Despite shared inventors, similar subject matter and a common assignee, the U.S. Court of Appeals for the Federal Circuit held that the prosecution history of one patent does not bar equivalents for claims of another patent where the two patents share no formal relationship and were presented to the patent office as patentably distinct inventions. Abbott Labs. v. Dey, 2002 U.S. App. LEXIS 7484 (Fed. Cir., April 23, 2002).

Abbott sued Dey for infringement of U.S. Patent No. 4,397,839 and U.S. Patent No. 4,388,301. The '839 patent resulted from continued research on lung surfactant compositions performed by one of the co-inventors of the '301 patent. The applications for the '839 and '301 patents were filed as separate and independent cases; but were co-pending, commonly assigned, shared a common subject and a common inventor and were examined by the same examiner. While the claims of the two patents recited different but overlapping percentages of phospholipid content, the asserted claim of the '839 patent also claimed adding free fatty acids to the composition.

Abbott conceded that the accused drug did not literally infringe the claims of the '839 patent, as tests showed that the phospholipid content of the accused formulation were outside the claimed range of the '839 patent. While the district court agreed that the percentages of phospholipid used in the accused formulations were equivalent to those claimed in the '839 patent, it nonetheless granted the defendants summary judgment of non-infringement, citing Pharmacia. The district court further found that Abbott was precluded from relying on the doctrine of equivalents to establish infringement of the '839 patent based on the prosecution history of the '301 patent. The prosecution history of the '839 patent contained no amendments or arguments that would estop the patentee from claiming infringement under the doctrine of equivalents. Abbott appealed.

The Federal Circuit vacated and remanded, stating that the relationship between the two patents "is insufficient to render particular arguments made during prosecution of the '301 patent equally applicable to the claims of the '839 patent." The Court reasoned that...

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