The Federal Circuit delivered a precedential decision on June 30, 2025, in Eye Therapies, LLC v. Slayback Pharma, LLC, reversing the Patent Trial and Appeal Board's (PTAB) claim construction of U.S. Patent No. 8,293,742. The ruling establishes important precedent for how prosecution history can fundamentally alter the conventional meaning of patent claim language, particularly the transitional phrase "consisting essentially of."
Patent Dispute Centers on Brimonidine Eye Treatment
The '742 patent covers methods for reducing eye redness using brimonidine, with claims that recite "consisting essentially of" administering brimonidine to patients with ocular conditions. The patent's prosecution history proved crucial to the Federal Circuit's analysis, as the original claims used the broader "comprising" language before being amended during patent prosecution.
During the original patent examination, the examiner rejected the claims based on prior art that disclosed brimonidine in combination with other active agents for treating ocular conditions. In response, the applicant amended the claims to use "consisting essentially of" instead of "comprising" and argued that the amended claims "do not require the use of any other active ingredients in addition to brimonidine." The examiner subsequently allowed the claims, reiterating this argument.
PTAB's Initial Ruling Favored Broader Interpretation
Slayback Pharma challenged the patent's validity in an Inter Partes Review (IPR), disputing the scope of "consisting essentially of" as used in the claims. Eye Therapies argued that the phrase should be interpreted in light of the prosecution history to mean administering brimonidine as the sole active ingredient.
The PTAB rejected this narrow interpretation, instead ruling that the claimed method should only be closed to additional active ingredients that are required to perform the claimed method. Under this construction, the method would remain open to administering brimonidine alongside other active ingredients, provided those additional ingredients were not required for the claimed method's performance. Based on this broader claim construction, the PTAB concluded the claims were obvious and held all claims unpatentable.
Federal Circuit Establishes Prosecution History Precedence
The Federal Circuit sided with Eye Therapies, emphasizing that prosecution history can significantly alter conventional claim language meanings. The court acknowledged the traditional meaning of "consisting essentially of" as a partially open transitional phrase that typically allows minor additional elements that don't materially affect the claimed subject matter's basic and novel characteristics.
However, the court explained that patentees can alter this conventional meaning through specification redefinition or prosecution disclaimers. Citing Phillips v. AWH Corp., the Federal Circuit noted that prosecution statements can "inform the meaning of the claim language by demonstrating how the inventor understood the invention and whether the inventor limited the invention in the course of prosecution, making the claim scope narrower than it would otherwise be."
Definitional Language Proves Decisive
The Federal Circuit found particularly compelling the applicant's use of definitional language during prosecution. In one key argument, the applicant stated that the cited reference "does not teach any methods of treating any conditions by administering a pharmaceutical composition consisting essentially of brimonidine (i.e., a pharmaceutical composition which does not include any other active agents)."
The court analyzed the applicant's use of "i.e.," noting its often definitional usage in patent records. The Federal Circuit reasoned that in this context, "i.e." indicates "methods which do not include administering other active agents." This definitional usage demonstrated that the conventional meaning of "consisting essentially of" was incompatible with the more restrictive meaning the applicant intended.
Distinguishing Prior Precedent
The PTAB had analogized the case to Ecolab, Inc. v. FMC Corp., which involved a patent for sanitizing fowl with a solution "consisting essentially of peracetic acid." In Ecolab, the Federal Circuit rejected a restrictive interpretation that would have limited claims to solutions containing peracetic acid as the only antimicrobial agent, finding this construction irreconcilable with the patent specification's disclosure of other antimicrobial agents.
The Federal Circuit acknowledged that the '742 patent's specification describes compositions containing active ingredients beyond brimonidine, alongside embodiments describing brimonidine as the sole active ingredient. The court viewed these alternative embodiments as consistent with the original "comprising" language. However, the court concluded that the applicant's specific amendments and arguments, particularly the definitional use of "i.e.," required the more restrictive construction that precludes agents other than brimonidine.
Implications for Patent Prosecution Strategy
The decision underscores the substantial weight prosecution history carries in post-issuance claim construction. While transitional phrases typically maintain traditional meanings, this case demonstrates that the intrinsic record, including prosecution history and application specifications, can fundamentally alter such definitions.
The ruling serves as a reminder that statements made during patent prosecution can have significant unintended consequences in post-grant proceedings and litigation. Patent applicants may want to consider using traditional transitional terms that correspond with the intended scope of their arguments to avoid potential uncertainty in future patent disputes.
