When is Closed Claim Language Actually Open? When it is Part of a Markush Group!

by Joshua Goldberg (NATH, GOLDBERG & MEYER – USA)

In the recent case of Amgen v. Amneal Pharma, (Fed. Cir. 2019),, Amgen’s U.S. Patent No. 9,375,405 protects a drug formulation for treating hyperparathyroidism in particular situations sold under the trade name Sensipar with about $1b annual sales. Amgen sued Amneal, Piramal, and Zydus for infringement based upon the constructive infringement of them each filing ANDAs to obtain market approval for selling a generic version of Sensipar. The District Court ruled that Amneal’s proposed product would not infringe the ‘405 patent.

On appeal, the CAFC vacated the verdict for Amneal based on claim construction issues and returned the case to the District Court for further consideration.

The focus of the claim construction issue was on how to interpret the “Markush” group recited in the claims. Under long-standing US law, a patent applicant can effectively define and claim a genus by enumeration of species within the genus.  Ex parte Markush, 1925 CD 126 (Com. Pat. 1924). In this decision, the Commissioner for Patents concluded that there are “many instances in which a generic term covering a number of substances cannot properly be employed” and that a listing of alternatives may be the only way the applicant “may cover his real invention without filing a number of applications.” This decision resulted in the advent of Markush groups, still being used in common practice to this day. For example, a proper Markush group would be limited to “a component selected from the group consisting of A, B, C, D, and any combination thereof.”

In the present case, Amgen’s claims recited:

A pharmaceutical composition comprising: . . .

from about 1% to about 5% by weight of at least one binder selected from the group consisting of povidone, [HPMC], … , and mixtures thereof.

Amneal’s proposed product includes both HPMC and polyethylene glycol (PEG) as binders. The question, then, was whether the patent claims were limited to binders expressly recited in Markush group, or whether additional binders were also included within the scope of protection. The District Court had previously found the claim closed to additional binding agents, and thus no infringement by Amneal. On appeal, the CAFC disagreed, finding:

There is no language in Amgen’s claim indicating that every binder … in the claimed formulation must be within the Markush group[]. Instead, the claim recites “at least one” binder … “selected from the group consisting of” various excipients…The plain language of this claim requires “at least one” of the Markush members and certainly does not indicate that the only binders…in the claimed formulation are those listed in the groups. And we do not see a sufficient basis for a different conclusion in the specification or in the prosecution history we have recited. . . .

[The claim] 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 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. There is no such basis here.

Based on the CAFC’s logic, even though the Markush group uses the closed “selected from the group consisting of” language, the claim overall uses the open “comprising” transitional phrase. Accordingly, the CAFC indicated while any infringing product would need to include a binder from the claimed Markush group, other binders could also be present and still fall within the scope of the claim. Based on this broader claim construction, it is likely Amneal will be found to infringe Amgen’s patent claims.