In a significant reversal for the U.S. Patent and Trademark Office’s Patent Trial and Appeal Board (PTAB), in Eye Therapies, LLC v. Slayback Pharma, LLC the Federal Circuit on June 30, 2025, held that the Board erred in its construction of the transitional claim phrase “consisting essentially of” as used in Eye Therapies, LLC’s U.S. Patent No. 8,293,742. The court held that the phrase, as used in the patent’s claims, excludes the presence of any additional active ingredients besides brimonidine. Because the Board’s unpatentability determination hinged on the broader construction, the Federal Circuit reversed the claim construction, vacated the Board’s decision, and remanded for further proceedings.
This decision is a strong reminder that prosecution history can override the default interpretation of transitional phrases, even ones as settled as “consisting essentially of.” As Charles Gideon Korrell notes, the court emphasized the importance of context and statements made during prosecution in determining claim scope.
Background: The ’742 Patent and Its Claims
Eye Therapies’ ’742 patent claims a method of reducing eye redness by administering a low concentration of brimonidine, an alpha-adrenergic receptor agonist known for its vasoconstrictive properties. Independent claims 1 and 3 recite methods “consisting essentially of” administering brimonidine or a brimonidine-containing composition:
- Claim 1: Administering brimonidine at a concentration of 0.001–0.05% w/v.
- Claim 3: Administering a brimonidine-containing composition with a pH of 5.5–6.5, formulated as an ocular drop, and brimonidine at 0.001–0.025% w/v.
During prosecution, the patentee amended the claims from “comprising” to “consisting essentially of” to overcome anticipation by U.S. Patent No. 6,242,442 (“Dean”), which disclosed the co-administration of brimonidine and brinzolamide.
PTAB’s Construction and Obviousness Holding
In inter partes review (IPR2022-00142) initiated by Slayback Pharma, the PTAB interpreted “consisting essentially of” to allow additional active ingredients, so long as they did not “materially affect the basic and novel properties of the invention,” citing PPG Indus. v. Guardian Indus. Corp., 156 F.3d 1351 (Fed. Cir. 1998) and Ecolab, Inc. v. FMC Corp., 569 F.3d 1335 (Fed. Cir. 2009).
Applying that broader construction, the Board concluded that combinations of prior art references—Dean, Norden, and Gil—rendered the claims obvious because those references disclosed or suggested brimonidine in combination with other agents.
The Federal Circuit’s Reversal
The Federal Circuit held the PTAB erred by failing to give proper weight to the prosecution history. As the court explained, while “consisting essentially of” typically allows for unlisted components that do not materially affect the invention’s basic and novel characteristics, a patentee may redefine that scope through prosecution disclaimer or definitional language.
Eye Therapies did just that. To distinguish Dean, the applicant argued that the claims “do not require the use of any other active ingredients,” and used definitional language equating “consisting essentially of brimonidine” with “methods which do not include administering other active agents.” The examiner relied on this when allowing the claims.
The court found these prosecution statements to be more than just explanatory—they limited the claim scope. As Charles Gideon Korrell emphasizes, applicants cannot walk back claim scope limiting statements after securing allowance on the strength of those very assertions.
Distinguishing Ecolab and Claim Scope Implications
The Board’s reliance on Ecolab was misplaced. There, the patent specification disclosed multiple embodiments with and without additional antimicrobial agents, and the prosecution history did not signal a narrowing of “consisting essentially of.”
Here, by contrast, Eye Therapies’ applicant used “i.e.” (i.e., definitional) statements during prosecution to expressly equate the claim language with single-agent administration. Although some embodiments in the specification describe co-administration, that inconsistency did not override the clear disclaimers during prosecution.
This distinction is critical. The court noted that claim construction need not encompass all disclosed embodiments, especially when claims have been narrowed post-filing.
Obviousness: Vacated Due to Reliance on Erroneous Construction
Because the PTAB’s obviousness analysis relied heavily on its flawed construction, the court vacated the unpatentability determination. For example:
- The Board treated prior art combinations that included multiple active ingredients as relevant.
- It reasoned that other agents “do not materially affect” brimonidine’s action and therefore did not violate the “consisting essentially of” limitation.
But under the proper construction—excluding any additional active ingredients—those references no longer map cleanly onto the claims. The Board will now need to reassess whether a person of ordinary skill in the art (POSITA) would have been motivated to administer brimonidine alone to reduce eye redness.
As Charles Gideon Korrell observes, this case underscores the importance of revisiting the obviousness inquiry when claim construction shifts materially—particularly when prior art references disclose combinations that no longer fall within the claim scope.
Practical Takeaways
- Prosecution History Matters: Courts will enforce narrowing claim scope if an applicant made clear representations during prosecution to secure allowance.
- Transitional Phrases Are Not Always Standard: Even familiar phrases like “consisting essentially of” are susceptible to narrower readings when prosecution history demands it.
- Spec Discrepancies Are Not Fatal: A narrowed construction may exclude embodiments in the specification, particularly if amendments came later and were necessary for allowance.
- Revisiting Obviousness: A change in claim construction often necessitates remand—especially when the PTAB relied on broader scope to identify prior art overlaps.
Charles Gideon Korrell notes that this case provides a helpful reminder for patent prosecutors and litigators alike: careful language during prosecution can define the battlefield years later, and transitional phrases are not immune from contextual redefinition.