Mayne's efforts to successfully design around Abraxis' Diprivan® patents may have resulted in the issuance of a patent covering its own product, but were not successful in avoiding infringement of Abraxis' orange book-listed patents under the doctrine of equivalents. Companies seeking to avoid infringement by designing around patent claims are still challenged by the evolving contours of the flexible doctrine.

In Abraxis Bioscience, Inc. v. Mayne Pharma (USA), Inc., No. 06-1118 (Fed. Cir. Nov. 15, 2006), the Federal Circuit disagreed with a district court's determination of literal infringement based on an erroneous claim construction, but affirmed the judgment of infringement under the doctrine of equivalents notwithstanding.

Abraxis' '520, '355 and '356 patents in suit are directed to improved formulations of Diprivan® and Rapinovet®, anesthetics consisting of an injectable oil-in-water emulsion containing propofol as its active ingredient. Earlier formulations of the drug compositions were highly susceptible to microbial contamination, and so additional research led to the addition of disodium edentate ("edentate") to the formulation to retard microbial growth in the propofol formulation. Abraxis obtained patents and a new FDA approval on its improved composition. In an effort to avoid infringement, Mayne determined that the calcium trisodium salt of diethylenetriaminepentaacetic acid ("pentetate" or "DTPA") was a promising candidate as an antimicrobial agent and sought generic approval on that product. The district court construed the claimed "edentate" to mean "EDTA as well as compounds structurally related to EDTA regardless of how they are synthesized," and determined that Mayne's DTPA composition literally infringed the Abraxis patents.

On appeal, the federal circuit disagreed that edentate could be construed to include structural analogues other than salts. The specification only described salts of EDTA as useful in the invention, and further emphasized the uniqueness of edentate as the only successful antimicrobial agent. According to the court, "[t]hose statements are inconsistent with a definition of "derivatives" that includes structural analogs that can encompass a large number of non-derivative compounds." The court concluded in dictum that Mayne's DTPA did not literally infringe the claims directed to edentate compositions based on its narrower interpretation of "edentate."

However, the court affirmed the judgment of infringement under the doctrine of equivalents, based on its finding that the differences between the claimed DTPA and Mayne's EDTA were insubstantial. Under the function-way-result test, both DTPA and EDTA worked as antimicrobial agents in the same way, e.g., metal ion chelation. Mayne's argument that the "way" prong should be defined more narrowly was not supported by the patent and inconsistent with expert testimony and Mayne's own ANDA submission. Finally, the court determined that Abraxis did not surrender or waive coverage of all polyaminocarboxylates (including DTPA) as equivalents simply by focusing its claim and disclosure on EDTA.

Please visit http://media.aplf.org/resources/alert2006-61/abraxis.pdf for a copy of the case for your reference.

To discuss these topics further, please feel free to contact the author, Michael R. Dzwonczyk (mdzwonczyk@sughrue.com), at Sughrue Mion, PLLC in Washington DC, USA.

The information contained in this email is provided for informational purposes only and does not represent legal advice. Neither the APLF nor the author intends to create an attorney client relationship by providing this information to you through this message.

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