On June 30, 2025, the Federal Circuit issued a precedential decision in Eye Therapies, LLC v. Slayback Pharma, LLC,[1] reversing the Patent Trial and Appeal Board’s (PTAB’s) claim construction of the phrase “consisting essentially of,” as recited in the claims of issued U.S. Patent No. 8,293,742 (hereafter, “the ’742 patent”).
1. A Refresher: “Open” Versus “Closed” Claim Language
Under the conventional claim construction doctrine, the transitional phrase “comprising” signals that the claim is open to additional elements or steps beyond those explicitly recited in the claim, whereas “consisting of” signals that the claim is limited to the exact elements recited therein and nothing more. In contrast, “consisting essentially of” signals that a claim is partially open. Typically, when “consisting essentially of” is used, the claimed subject matter is primarily composed of the explicitly recited elements, but may also include other, minor elements that do not materially affect the claimed subject matter’s basic and novel characteristics.
2. The “Consisting Essentially of” Language at Issue in the ’742 Patent
The ’742 patent is directed to methods for reducing eye redness using brimonidine. The claimed methods recite the “consisting essentially of” transitional phrase, such as in “[a] method for reducing eye redness consisting essentially of”[2] (emphasis added) administering brimonidine to a patient having an ocular condition. Of note, the claims originally recited the open “comprising” language. During prosecution, the examiner rejected the claims as allegedly being anticipated by a reference that disclosed brimonidine in combination with another active agent for treating ocular conditions. In response, Applicant amended the claims to recite “consisting essentially of” in place of “comprising,” and argued that, in contrast to the cited reference that required brimonidine in combination with another active ingredient, the amended claims “do not require the use of any other active ingredients (emphasis added) in addition to brimonidine.”[3] The examiner shortly thereafter allowed the claims, reiterating Applicant’s argument that the claims “do not require the use of any other active ingredients (emphasis added) in addition to brimonidine.”[4]
3. The PTAB’s Claim Construction
Slayback challenged the patentability of the ’742 patent in an IPR, during which the parties disputed the scope of “consisting essentially of” as recited in the claims. The Patent Owner, Eye Therapies, argued that the phrase should be read in light of the prosecution history, meaning that “consisting essentially of” in this context refers to a method for administering brimonidine as the sole active ingredient. The PTAB rejected this argument, contending that in view of both the conventional meaning of the phrase and the prosecution history, the claimed method should be read as only being closed to additional active ingredients that are required to perform the claimed method. As such, the claimed method would be open to administering brimonidine in addition to other active ingredients as long as the other active ingredients are not required to perform the claimed method. Based on this claim construction, the PTAB concluded that the claims are obvious in view of the prior art and held all claims unpatentable.
4. The Federal Circuit’s Claim Construction
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- Prosecution History Can Alter a Phrase’s Conventional Meaning
The Federal Circuit sided with Eye Therapies in construing the claims. The court first acknowledged the conventional meaning of “consisting essentially of.” The court then explained that a patentee can alter the phrase’s conventional meaning by redefining it in the specification or disclaiming an alternative meaning during prosecution. Quoting Phillips v. AWH Corp., 415 F.3d 1303, 1317 (Fed. Cir. 2005), the court expounded that statements made during prosecution 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.”
- The Prosecution History Leading to the ’742 Patent Informs an Atypical Meaning of “Consisting Essentially Of”
The Federal Circuit explained that the prosecution history informs an atypical meaning of “consisting essentially of” in the ’742 patent. As described above, during prosecution, Applicant amended the claims to recite “consisting essentially of” to distinguish over the cited art. According to the Federal Circuit, this prosecution history supports a “more restrictive interpretation” of the transitional phrase than its conventional meaning.[5] The court noted: “[w]hereas an interpretation applying the standard meaning might permit additional unlisted active ingredients, the applicant persuaded the examiner of the novelty of the claims by underscoring the absence of other active ingredients in the claimed methods.”[6]
The Federal Circuit also examined additional arguments made during prosecution. In one example, Applicant argued 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)” (emphasis added).[7] The court analyzed Applicant’s use of “i.e.,” noting that its usage in the intrinsic record is often definitional. The Federal Circuit reasoned that in this context, “i.e.” indicates “methods which do not include administering other active agents.”[8] In view of this definition, the court noted that the conventional meaning of “consisting essentially of” is incompatible with the more restrictive meaning that Applicant intended.
- Application of Ecolab, Inc. v. FMC Corp., 569 F.3d 1335 (Fed. Cir. 2009)
In the PTAB’s decision, the Board analogized the facts of this case to Ecolab, which concerned a patent directed to a method for sanitizing fowl with a solution which “consists essentially of . . . peracetic acid.”[9] In Ecolab, the Federal Circuit rejected a more restrictive interpretation of “consisting essentially of” that would have limited the claim scope to solutions containing peracetic acid as the only antimicrobial agent. The Federal Circuit found this narrower claim construction irreconcilable in view of the patent’s specification, which disclosed exemplary solutions containing antimicrobial agents other than peracetic acid.
The Federal Circuit acknowledged that the ’742 patent’s specification describes compositions containing active ingredients other than brimonidine, in addition to embodiments that describe brimonidine as the only active ingredient. The Federal Circuit viewed these alternative embodiments as making sense in view of the “comprising” language that the claims originally recited. Even with these alternative disclosures, however, the court reasoned that Applicant’s amendments and arguments, particularly the definitional use of “i.e.,” require a more restrictive construction of “consisting essentially of.” In this regard, the court concluded that the appropriate interpretation of the issued claims precludes the use of agents other than brimonidine.
5. Takeaways
This case underscores the weight that prosecution history can have on post-issuance claim construction. Although certain transitional phrases may often take on a traditional meaning, this case demonstrates that the intrinsic record (e.g., prosecution history and/or application specification) can alter such traditional definitions. To avoid potential uncertainty, applicants may want to consider using a traditional transitional term or phrase in their claims that corresponds with the scope of their arguments. Regardless, this case is a good reminder that whatever is stated in the record may have unintended consequences in post-grant proceedings and litigation.
[1] Eye Therapies, LLC v. Slayback Pharma, LLC, No. 2023-2173 (Fed. Cir. June 30, 2025).
[2] See claims 1 and 3 of U.S. 8,293,742.
[3] Page 6, July 19, 2011 Office Action Response dated October 19, 2011 in Pat. App. No. 12/460,941.
[4] Page 3, Notice of Allowance dated January 30, 2012 in Pat. App. No. 12/460,941.
[5] Eye Therapies, LLC v. Slayback Pharma, LLC, p. 8.
[6] Id. at 8–9.
[7] Page 8, July 19, 2011 Office Action Response dated October 19, 2011 in Pat. App. No. 12/460,941.
[8] Eye Therapies, LLC v. Slayback Pharma, LLC, p. 9.
[9] See U.S. Pat. No. 5,632,676.
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