Federal Circuit Affirms Finding That Mayne Pharma Infinges Abraxis Bioscience's Patent on Diprivan
Last week the U.S. Court of Appeals for the Federal Circuit affirmed a district court's finding that Mayne Pharma's ANDA for generic Diprivan (propofol) infringes Abraxis Bioscience's U.S. Patent No. 5,714,520 (and two other related patents). The '520 patent covers improved formulations of Diprivan, an injectable drug used to induce and maintain general anesthesia and sedation in patients. Specifically, the patent claims a propofol formulation containing edetate, an antimicrobial preservative. Mayne filed its ANDA for a propofol formulation containing a different preservative, the calcium trisodium salt of pentetate (also referred to as DTPA), and obtained a patent on the formulation.
In an opinion written by Judge Lourie for a unanimous panel, the Federal Circuit affirmed the district court's finding of infringement under the doctrine of equivalents (DOE). The most interesting aspect of the opinion addressed Mayne's argument that the district court improperly defined the "way" prong of the familiar function-way-result test of DOE infringement. The district court found that the "way" edetate works is by metal ion chelation. Mayne asserted that the proper definition of "way" was narrower: one that incorporates the specific metal ions that are chelated, the strength of the bonds that are formed during chelation, and stability constants.
According to the Federal Circuit:
"What constitutes equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case." [citing Graver Tank] . . . Here, the district court properly assessed the "way" edetate works by referring to the patent and the evidence presented at trial. The record evidence supports the conclusion that the "way" in which both edetate and calcium trisodium DTPA perform as an antimicrobial agent is by metal ion chelation.
While the Federal Circuit reversed the district court's claim construction as to the term "edetate" and its finding of literal infringement, its affirmance of the lower court decision under the doctrine of equivalents was sufficient to doom Mayne Pharma's case. It appears that Mayne must now wait until expiration of the patents in suit before it can market its generic propofol product.
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