The U.S. Court of Appeals for the Federal Circuit reversed the district court's claim construction and holding of literal infringement, but affirmed its holding that Mayne's generic product infringed Abraxis' (formerly AstraZeneca's) three patents covering DIPRIVAN. Abraxis Bioscience, Inc. v. Mayne Pharma (USA) Inc., Case No. 06-1118 (Fed. Cir., Nov. 15, 2006) (Lourie, J.).
This patent case revolved around a preservative called edetate (or EDTA) found to be "unexpectedly effective in retarding microbial growth," thereby preventing post-operative infections resulting from the infusion of the anesthetic DIPRIVAN. Abraxis filed suit following Mayne's Abbreviated New Drug Application (ANDA) submission for a generic version of DIPRIVAN including a structural derivative of EDTA called calcium trisodium salt of diethylene triamine pentaacetic acid (DTPA). Each patent claim asserted by Abraxis included the claim element "edetate," which the district court construed as "EDTA as well as compounds structurally related to EDTA regardless of how they are synthesized." Consequently, the court found that Mayne's compositions including the structural analog, DTPA, met this claim element and infringed literally and under the doctrine of equivalents.
Even though the Court agreed that the patentee had specially defined edetate in the specification as EDTA and derivatives thereof, it disagreed with the district courts' extension of EDTA "derivatives" to include, within the literal claim scope, EDTA structural analogs. Instead, the Court found that the definition of edetate should be limited to "the salts or anions of EDTA," which is consistent with the undisputed ordinary meaning of the term, as well as the intrinsic evidence. In particular, the Court relied upon examples in the specification describing EDTA salts useful in the invention and noting that none of the examples were structural analogs. Further, the Court relied upon the fact that the unexpected microbial properties related to edetate salts only, and not to a large number of derivative compounds. Given that Abraxis admitted during oral argument that "DTPA is not a edetate salt," the Court reversed the district court's finding of literal infringement by Mayne.
Although the Court limited the literal scope of the term edetate, it found that Mayne's composition including DTPA did fall within the scope of equivalents because it indisputably performed in broadly the same way in the composition as edetate -- to sequester metal ions to retard microbial growth. Further, the patentee did not limit or surrender claim scope during prosecution, where the patentee could have attempted to obtain claims to polyaminocarboxylic acids, a broad class of structural analogs including EDTA and DTPA. The Court found that the unforseeability of DTPA's efficacy supported a lack of disclaimer by the patentee. Further, the Court did not find error in the district court's determination that the separate patentability Mayne's composition with DTPA did not outweigh evidence of the substantial similarity between EDTA and DTPA which support the finding of equivalence.
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