CAFC Says Insubstantial Differences the Test for Chemical DOE

By: Andreas Baltatzis  |   May 26, 2017

Overview: The CAFC expressly endorses the “substantial differences” test for applying the doctrine of equivalents to chemical patents, bringing clarity to "sparse and confusing case law."

The Court of Appeals for the Federal Circuit (CAFC) recently examined the application of the Doctrine of Equivalents (DOE) in a chemical case in Mylan Institutional LLC v. Aurobindo Pharma Ltd., No. 2017-1645 (Fed. Cir. 2017).[1] This is the CAFC’s the first examination of the DOE in a substantial sense since addressing “vitiation” Deere & Co. v. Bush Hog LLC, 703 F.3d 1349 (Fed. Cir. 2012), and has particular import for applying the Graver Tank/Warner-Jenkinson framework for chemical cases.[2] The CAFC itself noted “the sparse and confusing case law concerning equivalents, particularly the paucity of chemical equivalence case law” and found an opportunity to “bring more clarity on these subjects.” No. 2017-1645 at 12.

The CAFC laid out the function-way-result (FWR) test and the insubstantial differences test as two equivalent tests to be applied in the alternative. See id. at 13.[3] The CAFC then reviewed then district court’s application of the FWR test, requiring that each of the function, way, and result aspect of the test be explicitly and individually addressed. Id. at 14. The decision was reversed and remanded due to the failure of the district court to adequately address the “way” aspect of the test. Id. at 16. In doing so, the CAFC stated that “the FWR test may be less appropriate for evaluating equivalence in chemical compounds if it cannot capture substantial differences between a claimed and accused compound.” Id. at 17 (emphasis added). The appeals court continued to endorse the substantial differences test for chemical compounds stating that “the substantial differences test may be more suitable than FWR for determining equivalence in the chemical arts.” Id.

Applied to the specific facts, the CAFC stated that:

[t]he district court found that the accused process using manganese dioxide was equivalent to the claimed process using silver oxide. But the court failed to consider whether the key reagent in the process, manganese dioxide, was substantially different from the claimed reagent, silver oxide, and hence whether the substitution for, and omission of, silver oxide left the accused infringer outside of the bounds of the claims.

Id. at 17-18. The CAFC then provided specific instructions to the district court to reapply the FWR test, and then “also consider whether an evaluation of equivalence under the substantial differences test may be better suited to the particular facts of this case.” Id. at 18.

Moving forward, practitioners should focus on application of the “substantial differences” test for determining equivalency for chemical patent claims in opinion practice.


[2] Where the United States Supreme Court stated that “[w]e expect that the Federal Circuit will refine the formulation of the test for equivalence in the orderly course of case-by-case determinations, and we leave such refinement to that court's sound judgment in this area of its special expertise.” Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 40 (1997). Those more convivial times prior to the recent string of near-unanimous reversals of the CAFC’s “sound judgment.”

[3] Cf “In our view, the particular linguistic framework used is less important than whether the test is probative of the essential inquiry: Does the accused product or process contain elements identical or equivalent to each claimed element of the patented invention?” 520 40.