IP Alert: Federal Circuit Revises Guidance on Markush Claim Construction

When a claim uses both the terms “comprising” and “selected from the group consisting of,” how should that claim be construed? More specifically, if the claim specifies a component “selected from the group consisting of” A, B, or C, and the accused product includes component A and component D, is there infringement? An earlier Federal Circuit case, Multilayer Stretch Cling Film Holdings, Inc. v. Berry Plastics Corp., discussed here, suggested that the answer to this question might be “no.” But on January 7, in a unanimous opinion in Amgen Inc. v. Amneal Pharmaceuticals, the Federal Circuit concluded that the answer was “yes,” at least under the facts before the court.

Amgen sued three generic drug manufacturers asserting infringement of U.S. Patent No. 9,375,405, which is directed to Amgen’s SENSIPAR? medication. Claim 1 of the ’405 patent recites both a “binder” and a “disintegrant,” each defined using Markush groups—“selected from the group consisting of.” But the claim is generally drafted as a “comprising” claim, which is open to other elements. In pertinent part, claim 1 recites as follows:

A pharmaceutical composition comprising:

. . .

(c) from about 1% to about 5% by weight of at least one binder selected from the group consisting of povidone, hydroxypropyl methylcellulose, hydroxypropyl cellulose, sodium carboxymethylcellulose, and mixtures thereof; and

(d) from about 1% to 10% by weight of at least one disintegrant selected from the group consisting of crospovid[o]ne, sodium starch glycolate, croscarmellose sodium, and mixtures thereof,

wherein the percentage by weight is relative to the total weight of the composition. . . .

Amneal’s accused formulation includes hydroxypropyl methylcellulose, one of the binders that is listed under claim 1’s Markush group, but also polyethylene glycol 400 and polyethylene glycol 8000, which are binders not listed under the Markush group. In district court, Amgen argued that the Markush groups in parts (c) and (d) should be open to non-recited elements. The district court held Amneal not to infringe, relying on the Multilayer decision to rule that Amgen had not overcome the very strong presumption that claimed Markush groups are “closed to unrecited binders and disintegrants.” Similar issues were presented for the other defendants’ products.

On appeal, Amgen challenged the district court’s “closed” interpretation of the (c) binder and (d) disintegrant limitations of claim 1. More specifically, Amgen argued that the “consisting of” Markush groups in (c) and (d) do not foreclose inclusion of unclaimed binders and disintegrants because the preamble of claim 1 includes the term “comprising,” and the term “consisting of” restricts only the scope of a particular Markush group. Conversely, relying on both Multilayer and another case, Shire Development, LLC v. Watson Pharmaceuticals, Amneal and the other generic manufacturers argued that the district court’s construction was correct because Amgen had not overcome the strong presumption that a claim term set off with “consisting of” is closed to unrecited terms.

The Federal Circuit began by holding that Multilayer and Shire do not address the question of interpretation of a claim including a “comprising” transitional phrase followed by a “consisting of” Markush limitation. The court noted that Multilayer and Shire addressed the question of interpreting a Markush group itself as open or closed.

The court then held that claim 1 of the ’405 patent did not preclude binders and disintegrants not meeting the claimed Markush groups in parts (c) and (d). More generally, the court held that a claim including a “comprising” transitional phrase followed by one or more “consisting of” Markush groups is met by an accused product containing components meeting the Markush groups. But such a claim does not preclude infringement by products including additional components functionally similar to the Markush limitations, unless the claim language or intrinsic evidence precludes construction including the additional components. 

After observing that the claim recites “at least one” binder or disintegrant “selected from the group consisting of” various excipients, the court concluded that “the limitations merely require that those particular binders or disintegrants meet the specified weight-percentage requirements, which is not inconsistent with the overall composition containing other binders or disintegrants.” Additionally, “[t]he plain language of this claim requires ‘at least one’ of the Markush members and certainly does not indicate that the only binders and disintegrants in the claimed formulation are those listed in the groups.”   

Put another way, so long as the specified binder or disintegrant was within the specified weight range, the claim permitted the presence of other binders and disintegrants. “Without more,” the court concluded, “such language is satisfied when an accused product contains a component that is from the Markush group and that meets the limitation’s requirements for the component. It does not forbid infringement of the claim if an additional component is present and functionally similar to the component identified in the Markush group limitation, unless there is a further basis in the claim language or other intrinsic evidence for precluding the presence of such additional components.”

In a secondary holding, the court rejected Amgen’s attempt to avoid the estoppel effect of a claim amendment during prosecution via reliance on general disclaimer language. Specifically, after an examiner’s amendment, Amgen relied on its own boilerplate language, submitted eight months after the examiner’s amendment, stating “[t]hese amendments have not been made in response to a prior art rejection but rather to place the claims in proper format and to better define the claimed subject matter, including equivalents.” The court rejected this effort, concluding that “[i]t is unclear what, if any, insight this conventional boilerplate statement provides into the reasons for the Examiner’s Amendment.”

The Amgen decision highlights the importance of carefully drafting and interpreting Markush claim limitations and also indicates some lack of clarity in the law for interpretation of such claims. It is uncertain, for example, what “further basis in the claim language” or “other intrinsic evidence” might cause the claim to be construed more narrowly. It is likely that further case law development will be necessary to elucidate this concept. Via the secondary holding, the court also signaled that it is inclined to view substance over form when considering amendments to claim scope during prosecution.

For more information on this decision, please contact Fitch Even attorney Giles N. Turner, author of this alert.

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