Consisting Essentially Of Trouble

10 March 2020 PharmaPatents Blog
Authors: Courtenay C. Brinckerhoff

The Federal Circuit decision in HZNP Medicines LLC v. Horizon Pharma USA, Inc. is a good reminder that even standard “patent lingo” can cause trouble down the line. Now that the court has denied rehearing en banc (with Judges Lourie, Newman, O’Malley, and Stoll dissenting), practitioners should be aware of the risks of invalidity for indefiniteness that may arise from the “consisting essentially of” transitional phrase used in claim drafting. 

Transitional Phrases

In patent lingo, the “transitional phrase” is the term or phrase that links the preamble of a claim to the body of the claim. The USPTO’s Manual of Patent Examining Procedure explains the meaning of the three standard transitional phrases in MPEP § 2111.03

The broadest and most commonly used transitional phrase is the term “comprising,” which is an “open-ended” term that “does not exclude additional, unrecited elements or method steps.” 

Method claims before the court in HZNP used “comprising” as a transitional phrase:

10. A method for applying topical agents to a knee of a patient with pain, said method comprising:
applying a first medication consisting of a topical diclofenac preparation to an area of the knee of said patient to treat osteoarthritis of the knee of said patient …;
waiting for the treated area to dry;
subsequently applying a sunscreen, or an insect repellant to said treated area after said treated area is dry …; and
wherein said subsequent application occurs during a course of treatment of said patient with said topical diclofenac preparation.

U.S. Patent No. 8,546,450, claim 10. 

(The patents at issue were listed in the Orange Book for Horizon’s PENNSAID® (diclofenac topical 2% solution) product.)

The narrowest transitional phrase is “consisting of,” which “excludes any element, step, or ingredient not specified in the claim,” with some narrow exceptions.

In between these two extremes is the transitional phrase “consisting essentially of,” which by definition “limits the scope of a claim to the specified materials or steps [recited] and those that do not materially affect the basic and novel characteristics of the claimed invention.”

Composition claims before the court in HZNP used “consisting essentially of” as a transitional phrase: 

49. A topical formulation consisting essentially of:
1-2% w/w diclofenac sodium;
40-50% w/w DMSO;
23-29% w/w ethanol;
10-12% w/w propylene glycol;
hydroxypropyl cellulose; and 
water to make 100% w/w, 
wherein the topical formulation has a viscosity of 500–5000 centipoise.

U.S. Patent No. 8,252,838, claim 49. 

Although “consisting essentially of” has a defined meaning, its definition raises two issues: what the “basic and novel characteristics of the claimed invention” are and what unspecified materials or steps would “materially affect” them. The decision in HZNP focused on indefiniteness surrounding the first issue. The judges dissenting from the denial of rehearing en banc would have left both issues to be decided on a case-by-case basis in view of a specific accused infringing product or method. During examination, examiners tend to focus on these issues in the context of specific prior art. 

The Federal Circuit Decision

The panel majority decision in HZNP was authored by Judge Reyna and joined by Chief Judge Prost. Judge Newman dissented in part, including on the issues surrounding “consisting essentially of.”

Addressing the indefiniteness challenge to the “consisting essentially of” claims, the district court had identified five properties discussed in the patents: (1) better drying time; (2) higher viscosity; (3) increased transdermal flux; (4) greater pharmacokinetic absorption; and (5) favorable stability. The indefiniteness ruling focused on the “better drying time” property, because the district court had found that “the specification described two different methods for evaluating” drying time that “did not provide consistent results.” 

The panel majority first upheld the district court’s reasoning that the Nautilus standard for assessing indefiniteness applies to the “basic and novel characteristics” inquiry of a “consisting essentially” of claim:

Having used the phrase “consisting essentially of,” and thereby incorporated unlisted ingredients or steps that do not materially affect the basic and novel properties of the invention, a drafter cannot later escape the definiteness requirement by arguing that the basic and novel properties of the invention are in the specification, not the claims [and so beyond the reach of the Nautilus standard].


[In accordance with Nautilus,] the basic and novel properties must be sufficiently definite so as to inform, with reasonable certainty, a POSITA of their scope within the context of the invention. 

The panel majority next agreed with the district court that the disclosure in the specification of two different methods for evaluating “better drying time” that evaluate drying time at different time frames after application rendered the claims indefinite: 

Here, an evaluation of the specification reveals inconsistencies about the basic and novel property of “better drying time.” Two tests are disclosed, but those tests do not provide consistent results upon which a POSITA would be able to evaluate “better drying time.” Consequently, we conclude that the district court did not err in its determination that a POSITA would not know under what standard to evaluate the drying rate of the invention, thus rendering the basic and novel property of “better drying rate” indefinite.

(I am not sure I agree with any opinion’s characterization of the specification ….)

Judge Newman’s Dissent 

Judge Newman’s dissent criticized the panel majority for importing the “better drying time” feature discussed in the specification into the claims and for holding that feature to the Nautilus standard:

Whatever the significance of drying time as an advantage of the claimed composition, recitation and measurement of this property in the specification does not convert the composition claims into invalidating indefiniteness because the ingredients are listed in the claims as “consisting essentially of.”

In her opinion, the panel majority’s approach departed “from long-established law and long-understood practice.”

The Dissent From Denial Of Rehearing En Banc

The dissent from the decision denying rehearing en banc was authored by Judge Lourie, and joined by Judges Newman, O’Malley and Stoll. The opinion echoes the theme of Judge Newman’s dissent:

[B]etter drying time is not in the claim, and it is the claims that the statute requires be definite.


The advantages of the invention, its utility and its basic and novel properties, are not in the claims.


[T]he advantages of an invention and disclosure of how to make and use an invention are not to be incorporated into claims for purposes of evaluating their indefiniteness. It is the language of the claims that determines their definiteness.

Acknowledging that the claim language includes the “consisting essentially of” phrase, Judge Lourie’s dissenting opinion explains: 

The language at issue here, “consisting essentially of,” is clear, definite, language indicating that the constituents of a claim cannot include materials that affect the basic and novel properties of the claimed composition. 

According to Judge Lourie’s dissenting opinion, such “inconsistent” materials can be determined in litigation, when the claims are asserted against an accused product, and the issue “should boil down to a fact question”:

Certainly, such a claim should not be successfully asserted against a composition that contains materials that render the composition unfit for its stated purpose. But until a suit arises, one does not know what such an inconsistent material might be. That does not make the claim indefinite.


[T]he fact that one generally has to determine this question at trial does not make the claim indefinite. To hold to the contrary is to vitiate established usage that indefiniteness of claims is to be determined based on what the claim recites, not advantages cited in the specification.

Is This Breadth Indefinite?

An indefiniteness principle recognized in the MPEP is that claim breadth does not necessarily equate with indefiniteness. See, e.g., MPEP § 2173.02. The examination guidance for “consisting essentially of” claims focuses on breadth rather than indefiniteness. For example, MPEP § 2111.03 instructs that, “absent a clear indication in the specification or claims of what the basic and novel characteristics actually are,” examiners are to treat “consisting essentially of” as equivalent to “comprising.” According to the MPEP, when relying on a “consisting essentially of” transitional phrase to avoid prior art, it is the “Applicant’s burden to establish that a step practiced in a prior art method is excluded from his claims by ‘consisting essentially of’ language.”

In view of the decision in HZNP, practitioners should be prepared for increased scrutiny of “consisting essentially of” claims, especially where the specification does not clearly identify the “basic and novel characteristics” of the claimed invention and how to assess them. 

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