Federal Circuit reverses claim construction but affirms infringement

November 16, 2006
Post by Blog Staff

Abraxis Bioscience (formerly AstraZeneca) is the holder of three patents on an improved formulation of an anesthetic, DIPRIVAN?. Prior formulations had the problem of increasing postoperative infections. The inventors discovered that by adding disodium edetate as an antimicrobial agent. This addition allowed DIPRIVAN? to be administered for up to 24 hours without a significant increased risk of infection. Mayne Pharma wanted to produce a generic competitor to DIPRIVAN?. Its scientists decided to use calcium trisodium DTPA, a compound structurally similar to disodium edetate. After Mayne filed an Abbreviated New Drug Application (ANDA) with the FDA, Abraxis asserted that Mayne's generic infringed its patents. Details of the case after the jump.At issue was the construction of the term "edetate" used in the asserted patents. The district court found that edetate, as used in the patent claims, included edetate and structurally related compounds. Because calcium trisodium DTPA is structurally related to edetate, the district court found the patents literally infringed. In the alternative, the district court also found the patents infringed under the doctrine of equivalents, as calcium trisodium DTPA accomplishes the same function in the same way with the same result as disodium edetate. The Federal Circuit disagreed with the district court's claim construction, but ultimately affirmed the finding of infringement. Specifically, the court held that the patent's specification specifically defined "edetate" to mean "ethyleneeiaminetetraacetic acid (EDTA) and derivatives thereof." The question then became the meaning of "derivatives." The Federal Circuit stated that because the examples of derivatives given in the specification were all salts of EDTA rather than structural analogs, it was inappropriate to consider structural analogs "derivatives" of edetate as that term was used in the patent. As a result, Mayne's product did not literally infringe the patents. The court did affirm the finding of infringement under the doctrine of equivalents. Applying the commonly-used "function-way-result" test, the court found that calcium trisodium DTPA performed the same function in the same way with the same result as EDTA. Accordingly, the ultimate finding of infringement was upheld. This is an interesting case because the ultimate finding of literal infringement turned on the construction of a term not even found in the asserted claims, "derivatives." It shows that while defining claim terms in the specification can eliminate some issues in an infringement case, it may not be a cure-all for claim construction battles in litigation. Further, while ultimately Mayne was found to infringe, because of the way the patent was drafted, infringement ultimately had to be proven by equivalents instead of literally, which can generate additional problems, such as prosecution history estoppel. To read the complete decision, click here.

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