Unscrupulous Copyist, Beware the Doctrine of Equivalents

In Abraxis Bioscience, Inc. v. Mayne Pharma (USA), Inc., Case No. 06-1118 (Fed. Cir., Nov. 15, 2006), pharmaceutical company, Mayne Pharma, Inc. (Mayne), lost an appeal from a district court’s decision finding their infringing product was specifically designed to mimic their competitor’s improved anesthetic. But although Abraxis Bioscience, Inc. (Abraxis) ultimately won their patent infringement suite, it was a close call. The United States Court of Appeals for the Federal Circuit reversed the decision of the United States District Court for the Southern District of New York granting judgment of literal infringement but affirmed the lower court’s finding of infringement under the doctrine of equivalents.

The accused product, ultimately an infringing product, was a generic form of DIPRIVAN®- an anesthetic researched and developed by former Astrazeneca Pharmaceuticals LP, now Abraxis. DIPRIVAN® contains a preservative called edetate (or EDTA) for “retarding microbial growth” which helps prevent post-operative infections that may otherwise result from the infusion of the drug. Abraxis sought protection of their product through three different patents covering DIPRIVAN®.

Mayne developed a similar formula that substituted EDTA with diethyline triamine pentaacetic acid (DTPA), a structural derivative of EDTA. Ultimately, the suite revolved around the meaning of the word “edetate” and whether the claimed preservative disclosed in the specifications of the patents involved could include EDTA derivatives such as structural analogs. “Edetate” is the claimed element which the district court found to perform substantially the same function in substantially the same way to obtain the same result as DTPA.

In reversing the lower court’s decision on the literal infringement and claim construction issues, the United States Court of Appeals for the Federal Circuit took a closer look at the specifications to U.S. Patent 5,714,520 and ruled that “edetate and derivatives” should be limited to “the salts or anions of EDTA,” noting that although the specification in the patent listed several derivatives of EDTA suitable for the formula invention, none were structural analogs and all are salts. This narrower determination led the Court to conclude that the district court was clearly erroneous in finding that Mayne had developed a product which literally infringes the asserted claims of the patent in suite.

Fortunately for Abraxis, the Court affirmed the lower courts finding of infringement based on the doctrine of equivalence. Unlike claim construction, infringement under the doctrine of equivalents is a factual determination reviewed for clear error. The Court found that although the scope of the term edetate was limited (by the examples provided in the specifications), the lower court properly analyzed and ruled that Mayne’s formula using DTPA was well within the scope of equivalents because DTPA performs in broadly the same way as EDTA, noting that the way in which both edetate and DTPA perform as an antimicrobial agent is by sequestering metal ions to retard microbial growth.

Furthermore, the Court found that although the patent specification could have attempted to obtain claims to a broader class, such as structural analogs which would have included DTPA, because the effectiveness of DTPA was unforeseeable, the lack of a broader disclosure did not amount to a surrendered or waived coverage of all polyaminocarboxylates, the broader class of structural analogs.

The Court’s decision concludes by noting that “the doctrine of equivalents is designed to protect inventors from unscrupulous copyist and unanticipated equivalents,” (citing two other decisions), and highlighting the district court’s findings that calcium trisodium DTPA was specifically chosen by Mayne “for its structural similarities to edetate and the likelihood that it would match the product characteristics and stability profile of Abraxis’ improved DIPRIVAN® formulation.”

Saul Acherman
Attorney at Law