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Explore the latest in patent, trademark, and copyright cases on the Merchant & Gould LLP blog. Stay informed with expert insights on intellectual property law updates.

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Last week, the U.S. Court of Appeals for the Federal Circuit issued a precedential decision in <a href="https://www.cafc.uscourts.gov/opinions-orders/23-2173.OPINION.6-30-2025_2537409.pdf"><em>Eye Therapies, LLC v. Slayback Pharma. LLC</em>, No. 23-2173 (June 30, 2025)</a>, reversing the Patent Trial and Appeal Board’s construction of the term “consisting essentially of,” and vacating the Board’s obviousness finding.

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Appellant Eye Therapies owns U.S. Patent No. 8,293,742, which claims a method of treating eye redness using a medicine “consisting essentially of” brimonidine. As initially drafted, the claims used the open-ended transitional phrase “comprising,” but the claims were rejected as obvious over another patent that disclosed the use of brimonidine with brinzolamide to treat eye redness. Eye Therapy amended the claims to use “consisting essentially of” instead of “comprising” and argued that the new claims were nonobvious and novel because they “did not require the use of any other active ingredients.” Based on this argument, the examiner allowed the claims.

Appellee Slayback Pharma petitioned for inter partes review (“IPR”) of the ’742 patent. During the IPR, the Board applied the traditional construction of the phrase “consisting essentially of” to permit inclusion of components not listed in the claim, provided they do not materially affect the basic and novel properties of the invention. Based on this construction, the Board found the ’742 patent’s claims obvious over prior art disclosing use of brimonidine with other active agents, such as brinzolamide, that did not materially affect the novel properties of using brimonidine alone.

The Federal Circuit reversed. While the Court acknowledged the traditional interpretation of “consisting essentially of,” it also noted “a patentee can alter that typical meaning.” The Court concluded that Eye Therapies had done just that during prosecution of the ’742 patent when it argued that amending the claims to include “consisting essentially of” instead of “comprising” made the claims allowable because they “did not require the use of <em>any</em> other active ingredients.” The Court held that Eye Therapies, by making this argument, had elected a more restrictive interpretation of “consisting essentially of” that precluded use of other active agents. The Court was not dissuaded by the fact that its construction would not embrace all embodiments in the specification, reasoning that amendments made during prosecution to obtain patentability naturally can result in claims that do not cover all embodiments.

Because the Court reversed the Board’s claim construction, it also vacated the Board’s obviousness determination and remanded for consideration under the proper claim construction.

This blog post was co-authored by Bette Muirhead &amp; Korben Smart.

CAFC Permits Patentee to Narrow “Consisting Essentially of”

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