The Federal Circuit’s recent decision in Amgen Inc. v. Amneal Pharms. LLC, 945 F.3d 1368 (Fed. Cir. 2020) provides guidance on construing claims that recite Markush groups, particularly in combination with the open and closed transitional phrases, "comprising" and "consisting of," respectively.  The Court clarified that additional unrecited members of the Markush group are allowed when the recited group is preceded by “comprising,” and include qualifying language such as “at least one.” 

This decision arose from an appeal from the District Court of Delaware in an Abbreviated New Drug Application (ANDA) litigation involving Amgen’s formulation patent for Sensipar®, U.S. Patent No. 9,375,405 ('405 patent).

Amgen filed patent infringement suits against Zydus, Piramal, and Amneal in response to their ANDA filing seeking approval to market generic versions of Sensipar®.  Representative claim 1 of the '405 patent recites:

A pharmaceutical composition comprising:

(a) from about 10% to about 40% by weight of cinacalcet HCI (the active ingredient of Sensipar®) in an amount of from about 20 mg to about 100 mg;
(b) from about 45% to about 85% by weight of a diluent selected from the group consisting of microcrystalline, cellulose, starch, dicalcium phosphate, lactose, sorbitol, mannitol, sucrose, methyl dextrins, and mixtures thereof,
(c) from about 1% to about 5% by weight of at least one binder selected from the group consisting of povidone, hydroxypropyl methylcellulose (HPMC), 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 crospovidone, sodium starch glycolate, croscarmellose sodium, and mixtures thereof,
wherein the percentage by weight is relative to the total weight of the composition, and
wherein the composition is for the treatment of at least one of hyperparathyroidism, hyperphosphonia, hypercalcemia, and elevated calcium phosphorus product. (emphasis added)

At the district court, J. Goldberg bifurcated the infringement and the invalidity counterclaims and held a four-day bench trial on infringement.  The key issue in the infringement analysis was whether the binders (subsection (c)) and disintegrants (subsection (d)) in claim 1 include unrecited elements.  Relying on Multilayer Stretch Cling Film Holdings, Inc. v. Berry Plastics Corp., 831 F.3d 1350 (Fed. Cir. 2016), the district court held that the recited Markush groups are "closed to unrecited binders and disintegrants."

Amneal's product used Opadry as a binder.  Opadry comprises HPMC, polyethylene glycol 400, and polyethylene glycol 800. Claim 1(c) only lists HPMC in its Markush group.  Amneal's product used crospovidone and pregelatinized starch as a disintegrant. Claim 1(d) only lists crospovidone in its Markush group.  The district court held that because Amneal's proposed generic product contained materials that are not recited in the Markush groups of claim 1, Amneal did not infringe the '405 patent.

Amgen appealed the district court's holding and contended that claim 1 is open-ended because of the open transitional phrase "comprising” at the beginning of the claim.  Amgen further argued that since the "consisting of" terms in subsections (c) and (d) are preceded by "at least one," the Markush groups only limit the "at least one" binder or disintegrant.  In other words, the "comprising" language permits the inclusion of additional binders and disintegrants, as long as the composition includes at least one binder and one disintegrant recited in each respective Markush group and meets the recited percent limitations.

The Federal Circuit agreed with Amgen and reversed the district court's claim construction and finding of non-infringement with respect to Amneal.  The decision further distinguished earlier Federal Circuit cases, Multilayer and Shire Dev., LLC v. Watson Pharm., Inc., 848 F.3d 981 (Fed. Cir. 2017).  The Federal Circuit explained that even though the claims at issue in Multilayer and Shire also recite "comprising" followed by subsections reciting "consisting of . . . [Markush groups]," the decisions only held that the claim elements within the subsections are limited to the Markush group.  The Federal Circuit emphasized that Shire and Multilayer did not decide whether "comprising" allows additional elements outside of the recited Markush groups.

The Amgen decision further held that the "at least one" language indicates additional binders and disintegrants are allowed and is consistent with the "comprising" language in the claim.  On remand, the Federal Circuit instructed the district court to consider whether Amneal's generic product contains at least one binder and one disintegrant that meet the limitations in Amgen's claim 1(c) and (d), irrespective of whether additional binders and disintegrants are present in the generic product.

This decision sheds light on the construction of claims reciting both the open and closed transitional phrases, "comprising" and "consisting of," respectively.  Shire and Multilayer construed the term "consisting of" as limiting a claim element to members within the recited Markush group.  This decision clarifies that additional unrecited claim elements are allowed when the limited claim elements are preceded by the open phrase "comprising" and include qualifying language such as “at least one” preceding the Markush group.

A comparison of the claims at issue in Amgen, Multilayer and Shire illustrates the differences in claim language:

As for practice tips, practitioners should avoid use of strict Markush group language “selected from the group consisting of A, B, and C” without transitional open “comprising” language and qualifying language such as “at least one” or “one or more,” if the intent is to cover additional unrecited members.