U.S. courts have long recognized that a product or process which does not literally infringe a patent can nevertheless infringe under the "doctrine of equivalents" if it is equivalent to the claimed invention. The percentage of patent decisions from the U.S. Court of Appeals for the Federal Circuit (CAFC) that reference the doctrine of equivalents has steadily declined since 2000. See Figure 1 below. However, the following recent decisions have drawn new attention to this important doctrine, particularly as it applies to pharmaceutical and biotechnology inventions.

Figure 1

Mylan Institutional v. Aurobindo Pharma, No. 2017-1645 (Fed. Cir. May 19, 2017)

Mylan is an unusual case arising from the grant of a preliminary injunction based on application of the doctrine of equivalents. The CAFC acknowledged that court precedent on equivalents was "sparse and confusing" and stated that it would "attempt to provide more clarity" on the subject. To this end, the CAFC noted that the Supreme Court has set forth two tests for determining equivalency to the claimed invention: the "function-way-result" (FWR) test (whether the accused product performs substantially the same function, in substantially the same way, to obtain the same result) and the "insubstantial differences" test (whether the accused product or process is substantially different from what is patented). The CAFC also observed that the Supreme Court believes "non-mechanical cases may not be well-suited to consideration under the FWR test."

The district court in Mylan based its determination on the FWR test and concluded that Aurobindo’s process was equivalent to the patented process. The CAFC disagreed, holding that the district court improperly applied the FWR test. According to the CAFC, the district court correctly evaluated that the claimed and alleged equivalent chemical reagents had the same oxidation "function", but it did not address the "way" the oxidation was performed. And because the reagents had different oxidation strengths and oxidized in different ways, there was sufficient doubt to defeat the preliminary injunction. As such, Mylan suggests that the choice of test under the doctrine of equivalents may very well determine the outcome, with the insubstantial differences test potentially being more appropriate in the chemical arts.

Enzo Biochem v. Applera Corp., No. 2016-1881 (Fed. Cir. August 2, 2017; nonprecedential)

In Enzo, the CAFC affirmed the district court's determination that Applera did not infringe Enzo's patent under the doctrine of equivalents. Enzo's patent claims directed to a nucleic acid probe did not explicitly exclude detecting the probe by a signal generated from the probe itself ("direct" detection). However, the patent specification explained that "indirect" detection using a secondary chemical agent bound to the probe is superior to direct detection, which led to a claim construction that the claims only covered indirect detection.

The CAFC explained that "[a] party can show infringement under the doctrine of equivalents if every limitation of the asserted claim, including a limitation’s 'equivalent,' is found in the accused product" and the equivalent "differs from the claimed limitation only insubstantially." And since Applera's accused products used direct detection and the concept of equivalency cannot embrace a structure that is specifically excluded from the scope of the claims, the CAFC found no infringement.

Although recent trends at the CAFC suggest that patent infringement cases are more often decided on literal infringement, cases like Mylan and Enzo are a reminder that the doctrine of equivalents is still alive and remains a key consideration for all patent enforcement actions.