In Mylan Institutional LLC v. Aurobindo Pharma Ltd., the Federal Circuit offered some clarity to the “sparse and confusing case law” concerning the doctrine of equivalents in the chemical context.  In reviewing a preliminary injunction where the district court found a reasonable likelihood of infringement under the doctrine of equivalents, the Court suggested that the “insubstantial differences” test is better suited for evaluating equivalence in chemical compounds than the more common “function-way-result” (“FWR”) test.

The asserted patents claim a process for preparing isosulfan blue (“ISB”) by reacting a starting compound with silver oxide.  The patentee argued that the defendant’s process, which uses manganese dixode instead of silver oxide, infringed under the doctrine of equivalents because the reagents produced similar ISB yields.  The district court applied the FWR test, which considers whether the accused product performs “substantially the same function in substantially the same way to obtain the same result,” and found that because both reagents functioned by converting the starting compound to ISB and resulted in a similar product, the patentee was reasonably likely to prevail on infringement.

On appeal, the Federal Circuit held that the district court erred in its analysis.  First, the Court remarked that even if the FWR test was the appropriate test, the district court considered only the function and result prongs of the inquiry, and failed to address the “way” the reagent worked to create the ISB.  Specifically, the district court did not consider the different oxidation strengths of the claimed and allegedly equivalent reagents, and therefore failed to consider the whether the accused product performed “in substantially the same way” as the patented product. Second, the Court stated that the FWR test may be less appropriate for evaluating equivalency in the chemical arts when it does not adequately capture the differences between a claimed and accused product or process.  Instead, the Court recommended using the “insubstantial differences” test, which asks whether the accused product or process is substantially different than what is patented. As the Court explained:

[C]onsider the well-known compounds aspirin and ibuprofen, which chemists would not usually consider to be structural equivalents under the insubstantial differences test…[T]hese two compounds differ substantially in structure. However, the two compounds would seem to be substantial equivalents under the FWR test. They each provide analgesia and anti-inflammatory activity (“function”) by inhibiting prostaglandin synthesis (“way”) in order to alleviate pain, reduce fevers, and lessen inflammation (“result”). Thus, a compound may appear to be equivalent under the FWR test, but not under the substantiality of the differences test.

The Federal Circuit encouraged the district court to consider the insubstantial differences test on remand.

In addition to clarifying equivalents case law, the Federal Circuit seems to be advocating for an approach that favors non-infringement in the chemical context.  Moving forward, the decision could make it easier for ANDA-filers to show non-infringement under the doctrine of equivalents.