Abraxis Bioscience v. Mayne Pharma
Derivatives of EDTA, As Read in Light of the Specification, Included Salts But Not Structural Analogs.
On appeal to the CAFC, the court reversed a finding of literal infringement of Abraxis’s U.S. Pat. Nos. 5,714,520 (the ’520 patent) and 5,731,355 (the ’355 patent) upon finding that the district court (S.D. N.Y.) erred in the construction of the claim term “edetate.” However, the CAFC affirmed the district court’s finding of infringement under the doctrine of equivalents (DOE).
The technology at issue relates to a pharmaceutical composition (DIPRIVAN® – an injectible oil-in-water emulsion containing propofol, or 2,6-diisopropylphenol,used to induce and maintain general anesthesia and sedation in patients) having a edetate preservative for retarding microbial growth in a giving set.
In attempting to formulate a generic composition having a different preservative, Mayne identified the calcium trisodium salt of diethylenetriaminepentaacetic acid (pentetate), or calcium trisodium DTPA. Notably, Mayne’s researchers had stated that this preservative is structurally similar (a structural analog) to edetate, and was chosen to match the reference product characteristics and stability profile.
The district court construed “edetate” to mean “EDTA as well as compounds structurally related to EDTA regardless of how they are synthesized” based upon the specification definition of edetate as “EDTA and derivatives thereof.” The CAFC disagreed, and found this construction to be overly broad, based particularly on the interpretation of the term “derivatives.” The inventors listed several derivatives of EDTA suitable for the invention. All of these derivatives are salts of EDTA, and not structural analogs. When read in light of the entire specification, the court found that the listing of various EDTA salts limited the term “derivatives” to exclude structural analogs. Interestingly, the court pointed to a statement that edetate was “the only agent that would meet our requirements.” (Emphasis in opinion). Thus, the CAFC concluded that edetate is EDTA and derivatives of EDTA, such as salts, but not including structural analogs. Accordingly, there can be no literal infringement with use of DTPA as a preservative in the generic DIPRIVAN® formulation.
In affirming the DOE holding, however, the CAFC noted the traditional DOE standards. For example, “infringement may be found under the doctrine of equivalents if every limitation of the asserted claim, or its ‘equivalent,’ is found in the accused subject matter, where an ‘equivalent’ differs from the claimed limitation only insubstantially.” Also, under the function-way-result test for DOE, an accused device that “performs substantially the same function in substantially the same way to obtain the same result” as the patented invention may infringe under the doctrine. Furthermore, what constitutes equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case. Equivalence, in the patent law, is not the prisoner of a formula and is not an absolute to be considered in a vacuum.
The district court had concluded that calcium trisodium DTPA and edetate were equivalent after finding that the differences existing between the two were insubstantial. The district court identified the “function” of edetate as retarding microbial growth in propofol oil-in-water emulsions; the district court then defined the “way” that edetate worked as by metal ion chelation; and finally the district court found that the result achieved was retarding microbial growth to the extent required by the microbiological test set forth in the claims. The CAFC found this to be “well-reasoned” and not clearly erroneous (the standard for the DOE factual determination).
Notably, the CAFC rejected all of Maynes arguments regarding application of the DOE in this case. In particular, Abraxis was not barred from capturing DTPA, or any other polyaminiocarboxylate for that matter, as an equivalent just because they limited the claims to edetate. Abraxis did not disavow other polyaminiocarboxylates! A clear an unmistakeable surrender of subject matter is required to find such an estoppel.