Claim Interpretation Destroys Literal Infringement, But Not Equivalents

Abraxis Bioscience, Inc. v. Mayne Pharma (06-1118) - November 15, 2006

Mayne appealed a judgment of literal infringement and infringement under the doctrine of equivalents, arguing that the district court erred in the construction of the term "edetate," (EDTA) which is a limitation in each of the asserted claims.

This term was construed by the district court as "EDTA as well as compounds structurally related to EDTA regardless of how they are synthesized." Based on the district court’s construction of "edetate" as encompassing structural analogs of EDTA, the court found that Mayne’s generic propofol formulation infringed.

The Federal Circuit focused closely on the specification, and found that the inventors' definition of edetate listed several derivatives of EDTA that are suitable for the invention, but all of the listed derivatives were salts of EDTA, but not structural analogs. Other statements in the specification that listed agents as advantageous, preferable and "exceptional" convinced the court that the feature was limited to EDTA salts. One particular statement in the specification was noted by the court:

We then investigated the possible use of other agents which might have the action that we sought. We unexpectedly found that edetate, which is not regarded as a broad spectrum antimicrobial agent was the only agent that would meet our requirements.

This statement indicated that edetate possessed particular chemical properties that allowed it to work as an effective antimicrobial agent and that the term "derivatives" was not intended to extend broadly.

Since Mayne's use of DTPA was not a derivative or salt of EDTA, the court reversed the finding of literal infringement.

However, on the issue of doctrine of equivalents, the court upheld the finding of infringement. Performing the function-way-result test, the court concluded that DTPA performs substantially the same function in substantially the same way to achieve the same result as edetate. This was further supported by findings made by the district court that DTPA was specifically chosen for Mayne's generic propofol formulation because of its structural similarities to edetate and the likelihood that it would match the product characteristics and stability profile of Abraxis’ patented formulation.

The court also found that Abraxis did not clearly disavow DTPA by claiming edetate, since there was no evidence that the patentees made a "clear and unmistakable surrender" of DTPA during prosecution. In fact, the Federal Circuit agreed with the lower court that "the antimicrobial activity of calcium trisodium DTPA was unforeseeable during prosecution."

This is an interesting case, which underscores one of the major problems in patent law: claim interpretation. The claims in the patents for this case went through numerous stages of interpretation through filing, prosecution, litigation and appeal. In retrospect, this seems like a perfectly reasonable opinion. However, there's also a strong argument that anyone reading the patents and file wrappers prior to this case could not possibly have predicted this type of outcome.