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The Federal Circuit Rejects PTAB’s Use Of Traditional Construction Of “Consisting Essentially Of”
07/15/2025On June 30, 2025, the U.S. Court of Appeals for the Federal Circuit vacated a decision by the U.S. Patent Trial and Appeal Board (the “Board”) and remanded the case for further proceedings using a narrower construction of the phrase “consisting essentially of.” The Federal Circuit strayed from the traditionally broad construction of “consisting essentially of” because the evidence showed that the inventor clearly intended for the phrase to have a narrower meaning. Eye Therapies, LLC v. Slayback Pharma, LLC, No. 2023-2173, 2025 WL 1788409 (Fed. Cir. June 30, 2025).
Eye Therapies owns U.S. Patent No. 8,293,742 (the ’742 Patent), which teaches a method to reduce eye redness using a low-concentration dose of brimonidine. During prosecution, claims 1 and 3 originally utilized the transition phrase “comprising,” but the claims were rejected for lack of novelty. To overcome this rejection, “comprising” was amended to “consisting essentially of,” and the applicant successfully argued that the invention was different from the prior art because the only active agent utilized was brimonidine. In contrast, the prior art utilized brimonidine in conjunction with other active agents. The patent was then issued using “consisting essentially of.”
On petition by Appellee Slayback Pharma LLC, the Board completed an inter partes review of claims 1–6 of the ’742 Patent and found the claims unpatentable because they were obvious in view of the prior art. Claim construction focused on the meaning of “consisting essentially of,” with Slayback advocating for the traditional broader construction and Eye Therapies advocating for a narrower construction. The Board sided with Slayback and adopted the broader construction because there was not enough evidence to justify deviating from traditional construction. Using the traditional open construction, the claims were rejected because they were not novel over prior art that taught the use of brimonidine in addition to another active agent.
On appeal, the Federal Circuit held that the Board erred in its construction of “consisting essentially of.” In contrast to the Board, the Federal Circuit found strong evidence that supported deviating from the traditional construction.
“Consisting essentially of” is traditionally interpreted as an “open” transition phrase that requires the inclusion of the claimed limitation but does not preclude the inclusion of unclaimed elements. Under this construction, the claims of the ’742 Patent would require the presence of brimonidine but would not preclude the inclusion of other active agents. The Federal Circuit found the evidence was at odds with this traditional interpretation based on the arguments made during prosecution. Specifically, the evidence showed that the applicant had successfully shown patentability during prosecution by asserting that the prior art taught the use of brimonidine in addition to another active agent while the claimed invention used only brimonidine. Understanding the claims to preclude the use of active agents other than brimonidine, the examiner allowed the patent. Using the traditional construction would be contrary to both the applicant’s and the examiner’s understanding of the term when the patent issued, and thus the Federal Circuit departed from the traditional construction. Instead, the Federal Circuit construed “consisting essentially of” the same way the examiner and applicant understood it during prosecution, i.e., to preclude the presence of active agents other than brimonidine.
As the Board’s claim construction informed its analysis and subsequent invalidation of claims 1–6, the Board’s error in claim construction infected its finding of obviousness. Relying on the erroneous claim construction led the Board to consider methods that utilized other active agents in addition to brimonidine as prior art, but these methods fell outside the scope of the claims because the claims preclude the use of other active agents. Thus, the Federal Circuit vacated the Board’s findings and remanded the case for re-analysis using the Federal Circuit’s construction.
