Federal Circuit holds that transitional phrase “consisting essentially of” renders claim indefinite, unless the “basic and novel properties” of the invention are definite

HZNP Medicines LLC, Horizon Pharma USA Inc., v. Actavis Laboratories UT, Inc., HZNP v Horizon Pharma Appeal No. 2017-2149 et al, decided October 10, 2019 was an appeal from the District Court of New Jersey’s judgment of invalidity and noninfringement.  Amongst others, at issue was the District Court’s construction of the transitional phrase “consisting essentially of” in a formulation claim reciting 5 components and water to 100%, the composition having a specified viscosity.  To wit, the District Court held that a POSITA would be incapable of determining whether any additional non recited component would impact one of five identified basic and novel properties, i.e., better drying time,  and thus, held the claim indefinite for its recitation of “consisting essentially of”.  When asked to reconsider the holding, the District Court analyzed a second of the five identified basic and novel properties, i.e., “favorable stability” and also found the specification lacked “the requisite guidance for a POSITA to evaluate stability,” found the “favorably stability” property indefinite, thus by extension bolstering the Court’s conclusion that the phrase “consisting essentially of” was indefinite.

The Federal Circuit affirmed.  After noting that the parties did not dispute the legal meaning of the phrase, the majority stated:

By using the phrase “consisting essentially of” in the claims, the inventor in this case incorporated into the scope of the claims an evaluation of the basic and novel properties…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 indefiniteness requirement by arguing that the basic and novel properties of the invention are in the specification, not the claims. HZNP, slip opinion, page 24.

The Court explained:

Indeed, if a POSITA cannot ascertain the bounds of the basic and novel properties of the invention, then there is no basis upon which to ground the analysis of whether an unlisted ingredient has a material effect on the basic and novel properties.  HZNP, slip opinion, page 28.

The majority then found that the district court had not erred in determining that the basic and novel property “better drying time” and thus the transitional phrase “consisting essentially of” were indefinite and affirmed.

Even though the majority wrote:

Notably, the phrase “consisting essentially of” is not per se indefinite.  Indeed a patentee can reap the benefit of claiming unnamed ingredients and steps by employing the phrase “consisting essentially of” so long as the basic and novel properties of the invention are definite.


To be clear, we do not hold today that so long as there is any ambiguity in the patent’s description of the basic and novel properties of its invention, not matter how marginal, the phrase “consisting essentially of” would be considered indefinite.  Nor are we requiring that the patent owner draft claims to an untenable level of specificity.  We conclude only that, on these particular facts, the district court did not err in determining that the phrase “consisting essentially of” was indefinite in light of the indefinite in light of the indefinite scope of the invention’s basic and novel property of a ‘better drying time.”

Judge Newman was not consoled, stating in particular regarding the first quoted passage above “This statement is contrary to long-standing law and practice…” and “When the properties of a composition are described in the specification, the usage “consisting essentially of” the ingredients of the composition does not invalidate the claims when the properties are not repeated in the claims.”  HZNP, dissenting opinion, pages 5-6.  Instead, Judge Newman urged, the knowledge of the person of ordinary skill can be used to “fill any gap in proving the properties of compositions claimed in the “consisting essentially of” form.”  HZNP, dissenting opinion, page 2.  According to Judge Newman, contrary to precedent, the majority held that “composition claims are invalid unless they include the properties of the composition in the claims,” thereby creating a “new rule of claiming compositions [that] casts countless patents into uncertainty.”  HZNP, dissenting opinion, page 10.