Usually, it is the claim terms other than the transitional phrase that have an atypical meaning.
Patent claims are typically accorded their plain and ordinary meaning, and it is “well-settled that an inventor may act as his own lexicographer to define a patent term,” Ecolab, Inc. v. FMC Corp., 569 F.3d 1335, 1344 (Fed. Cir. 2009) (citing Phillips v. AWH Corp., 415 F.3d 1303, 1316 (Fed. Cir. 2005) (en banc)). But what is needed to demonstrate a patentee’s intention to reinterpret a term? Patentees might make their intended meaning of a term clear by including a particular definition in the specification.
Transitional phrases used in patent claims have varying degrees of open-endedness, with “comprising” being the most open and “consisting of” being the most restrictive. The transitional phrase “consisting essentially of” is typically interpreted as a middle ground in which the claimed invention necessarily includes the recited elements but is open to other elements that do not materially affect the novel properties of the claimed invention.
Usually, it is the claim terms other than the transitional phrase that have an atypical meaning.
However, as illustrated in the recent case of Eye Therapies, LLC v. Slayback Pharma, LLC, 141 F.4th 1264 (Fed. Cir. 2025), a patentee can also advance an atypical meaning of a claim term through statements, characterization and evidence in the prosecution history, and the claim term having the atypical meaning can be the transitional phrase.
Background and Procedural Posture
Eye Therapies owns U.S. Patent No. 8,293,742 (’742 patent), directed to a method for reducing eye redness using a low-concentration dose of brimonidine. The main independent claims recite methods “consisting essentially of administering brimonidine” or “consisting essentially of topically administering … a pharmaceutical composition consisting essentially of brimonidine … .” Slayback Pharma filed a petition for inter partes review (IPR), asserting that the ’742 patent was unpatentable on the grounds of obviousness. The Patent Trial and Appeal Board (PTAB) granted Slayback’s petition and instituted IPR proceedings.
During IPR, the PTAB had to decide the meaning of the transitional phrase “consisting essentially of” to determine whether the claimed invention included the use of additional active ingredients along with the low-concentration dose of brimonidine.
Eye Therapies argued that the transitional phrase “consisting essentially of” in the claims should be read as claiming brimonidine as the sole active ingredient and excluding other active ingredients in the invention, referring to the prosecution history of the ’742 patent to support their argument. During prosecution, the examiner rejected the claims as being obvious over a prior art reference disclosing a combination therapy with brimonidine and brinzolamide to treat ocular diseases. In response, Eye Therapies amended the claims, replacing “comprising” with “consisting essentially of” to distinguish the claims from the prior art because the prior art did not disclose a method utilizing brimonidine as the sole active ingredient. See Eye Therapies, 141 F.4th at 1267. The examiner, in allowing the claims, reiterated that Eye Therapies’ amendment meant that the claimed methods “do not require the use of any other active ingredients in addition to brimonidine.” Id.
The PTAB, however, in its final written decision held that “consisting essentially of” should retain its typical meaning—that in the context of the claimed invention, the invention necessarily includes the ingredients listed but is open to other nonessential ingredients. According to the PTAB in rejecting Eye Therapies’ arguments:
[U]nlike Patent Owner, we do not read the prosecution history as prohibiting the use of any other active ingredients besides brimonidine. To do so would construe the semi-open-ended transition phrase “consisting essentially of” to have the same scope as the closed transition phrase “consisting of.” Id.
The PTAB also noted that the ’742 patent’s specification stated that low-dose brimonidine alone could significantly reduce hypermia, and—citing Ecolab, Inc. v. FMC Corp., 569 F.3d 1335 (Fed. Cir. 2009)—reasoned that additional agents would “not materially affect the basic and novel characteristics of the invention.” Id. at 1268.
Accordingly, the PTAB concluded that the transitional phrase “consisting essentially of” used in the claims of the ’742 patent did not preclude additional active ingredients such that the claims were unpatentable as obvious in view of the prior art. Eye Therapies appealed the decision to the United States Court of Appeals for the Federal Circuit.
The Federal Circuit’s Decision
On appeal, Eye Therapies again pointed to the ’742 patent’s prosecution history as supporting an atypical meaning of the transition phrase “consisting essentially of.” Slayback, on the other hand, argued that the PTAB properly construed the phrase “consisting essentially of,” relying on Eye Therapies’ statements made during prosecution that the claims as amended “do not require” the use of active ingredients other than brimonidine, not that they preclude their use. See id. at 1271.
Disagreeing with Slayback, the Federal Circuit reversed the PTAB’s decision and held that the ’742 patent claims containing the phrase “consisting essentially of” had been redefined to exclude active ingredients other than brimonidine.
The Federal Circuit acknowledged that the transitional phrase “consisting essentially of” has long been understood as including components that are not listed in the claim, if they do not “materially affect the basic and novel properties of the invention.” Id. at 1269 (quoting AK Steel Corp. v. Sollac, 344 F.3d 1234, 1239 (Fed. Cir. 2003)). The court noted, however, that patentees can alter the typical meaning of a phrase by, for example, making the intended meaning clear in the specification. In particular, the court explained that statements during patent prosecution history can inform the claim language’s meaning and show how the inventor limited the invention’s claim scope during prosecution.
In this case, the Federal Circuit agreed with Eye Therapies that the prosecution history supported an atypical meaning of “consisting essentially of” in the ’742 patent. The court noted that an applicant’s explanatory remarks can demonstrate what the applicant meant by its amendment, thereby defining a claim term or limiting claim interpretation. Here, Eye Therapies “persuaded the examiner of the novelty of the claims by underscoring the absence of other active ingredients in the claimed methods.” Id. at 1270 (emphasis in original). Moreover, in explanatory remarks, Eye Therapies differentiated the claimed methods from the prior art by using “i.e.” to define “consisting essentially of” as not including “administering other active agents.” Id. Hence, the court found that Eye Therapies’ interpretation of the phrase “consisting essentially of” indicated a “more-restrictive-than-typical” interpretation. Id.
The Federal Circuit further clarified that Ecolab—a case that the PTAB cited to support its decision—was consistent with the court’s position. The court explained that in Ecolab, the argument for an alternative meaning of “consisting essentially of” was rejected because the overall prosecution history did not support the intention to adopt this atypical meaning. See Ecolab, 569 F.3d at 1343-44. Moreover, the patent specification in Ecolab provided examples that described compositions containing ingredients other than the ingredient listed in the claims. See id.
Although the ’742 patent specification in this case also contained embodiments describing compositions containing active ingredients other than brimonidine, the Federal Circuit maintained that the atypical meaning of “consisting essentially of” was still compatible with the embodiments that describe compositions with brimonidine as the only active ingredient. The court concluded, “The fact that [their] construction [did] not encompass all alternative embodiments [did] not foreclose its application.” Eye Therapies, 141 F.4th at 1271.
In rejecting Slayback’s argument that the claimed methods “do not require” other active ingredients rather than preclude their use, the court noted that Eye Therapies’ attempts to distinguish the claimed invention from the prior art by using a definitional use of “i.e.” to equate its claimed invention of “methods consisting essentially of administering brimonidine” with “methods which do not include administering other active agents” demonstrated that Eye Therapies intended “do not require” to mean precluding the use of active ingredients other than brimonidine. Id. at 1271.
Accordingly, the Federal Circuit concluded that the transition phrase “consisting essentially of” in the claims of the ’742 patent should be read as excluding the use of active ingredients other than brimonidine and reversed the PTAB’s claim construction.
On the issue of obviousness, the Federal Circuit found that the erroneous claim construction “infected” the PTAB’s obviousness analysis, subsequently vacating the PTAB’s decision and remanding the matter for the PTAB to determine the issue of obviousness under the correct claim construction.
Conclusion and Practice Points
Assertions as to the meaning of patent claim terms during prosecution may have more weight in claim construction during litigation than the plain and ordinary meaning of a patent claim term, including transitional phrases. In patent prosecution, practitioners should be keenly aware that what they say on the record may be determinative of how a claim term, including a transitional phrase, is later interpreted.
In contested proceedings, practitioners should be aware that a patent claim term may not be accorded its plain and ordinary or well-ascribed traditional meaning, as illustrated by Eye Therapies, where the prosecution history and statements made in support of a particular meaning—a transitional phrase—as part of the intrinsic evidence informed the court of how the claim term “consisting essentially of” should be construed. The use of explanatory remarks in prosecution to explain the term and the use of definitional terms such as “i.e.” supported the atypical meaning of a transitional phrase.
In Eye Therapies, the patentee prevailed on appeal at the Federal Circuit in obtaining a favorable claim construction based on the statements it made during prosecution in characterizing the scope of the claims. Practitioners should consider carefully the wording of and characterizations in arguments made before the USPTO during prosecution, as statements made during prosecution and the characterization of the nature of the claims can be used to ascribe atypical meanings to claim terms, including transitional phrases, and may ultimately define the meaning of the claims for the remaining term of the patent (for either the good of the patentee as in Eye Therapies or to the detriment of the patentee if a claim construction avoids including the activities or products of an accused infringer). Likewise, another takeaway from Eye Therapies is that in litigation, attention should be paid to the statements made during prosecution when advancing a claim construction.
For More Information
If you have any questions about this Alert, please contact Thomas J. Kowalski, Brandon A. Chan, Ph.D., any of the attorneys in our Intellectual Property Practice Group or the attorney in the firm with whom you are regularly in contact.
Disclaimer: This Alert has been prepared and published for informational purposes only and is not offered, nor should be construed, as legal advice. For more information, please see the firm's full disclaimer.