by Dennis Crouch
Amgen v. Amneal Pharma (Fed. Cir. 2020)
Amgen’s patent at issue covers a drug formulation for treatment of hyperparathyroidism in particular situations sold under the trade name Sensipar with about $1b annual sales. U.S. Patent 9,375,405. Note here, that Amgen’s primary patent on the blockbuster drug expired in 2018, but this secondary formulation patent has been effective at keeping generics off the market.
Amgen sued Amneal, Piramal, and Zydus for infringement based upon their ANDA filings with the FDA. The district court ruled that the Zydus proposal would infringe, but that the proposed formulations by Amneal and Piramal would not infringe. On appeal, the Federal Circuit has vacated the verdict for Amneal on claim construction, but affirmed no-infringement by Piramal and infringement by Zydus. Thus, Piramal has something of a green-light to move ahead.
A major portion of the appeal focused on proper construction of a Markush group that required a “binder”:
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.
‘405 patent claim 1.
The Markush Group claim form stems from a 1923 decision by the Commissioner of Patents that allowed a patent applicant to effectively define and claim a genus by enumeration of species within the genus. Ex parte Markush, 1925 CD 126 (Com. Pat. 1924). In Markush, the patent applicant attempted to claim a diazotized compound for making dyes that includes
material selected from the group consisting of aniline, homologues of aniline and halogen substitutes of aniline.
The applicant (Markush) had considered a broader descriptive genus such as “mono-amines” but concluded that to be too broad since it including too many non-working embodiments. The examiner though refused to examine the “alternative” claim form.
In his decision, the Commissioner in Markush 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.”
Note here that Amgen’s Markush group is remarkably similar to that presented by Markush’s patent attorney Victor Borst back in 1925. The claim format has remained remarkably “stuck” as a limited mechanism for avoiding claim-in-the-alternative objections.
Amneal’s binder includes HPMC as recited in the claims, but also includes polyethylene glycol (PEG). The major question in the case here is whether Amgen’s Markush Group is “open” or “closed.” In other words, does the presence of the additional compound in the binder (PEG) avoid infringement. The district court found the claim closed to additional binding agents and thus that Amneal does not infringe. On appeal, however, the Federal Circuit rejected the claim construction:
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. And 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. The 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. 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.
Slip Op. Thus, while the markush group itself may be closed (based upon its “consisting of” language), the claim as a whole is open (based upon its “comprising” transition in the claim’s introduction). With this broader claim interpretation, it looks like Amneal will be found to infringe.
Piramal’s proposed product is different in that its binder is a starch not listed in the Markush group. Thus, no literal infringement. Amgen unsuccessfully argued for infringement under the Doctrine of Equivalents. The problem was that the Markush group was added as part of a narrowing Examiner’s amendment that led to an allowance. (The group was already in a dependent claim — added to claim 1). Although the examiner asked for the amendment, Amgen argued on appeal that it wasn’t necessary to overcome the prior art because a separate amendment was sufficient. However, Amgen failed to provide an alternative purpose behind why the examiner asked for such an amendment. The Federal Circuit faulted that failure of alibi.
[I]f Amgen is correct … the Examiner proposed the Examiner’s Amendment for no purpose at all. Such a reading of the prosecution history is at best unpersuasive.
Slip Op. I’ll note here that the Federal Circuit appears shocked that an examiner would propose an amendment for no legitimate purpose. As a counterpoint, consider that a large portion of examiner rejections are later withdrawn by the examiner upon further consideration.
In any event, a narrowing amendment made for the purposes of securing the patent triggers a presumption of prosecution history estoppel that would prohibit a claim of equivalents to re-claim the narrowed subject matter. One way to get around this presumption is to show that the narrowing amendment is tangential to the equivalent in question. Here, however, the starch used by Piramal is the same starch disclosed in the prior art overcome by the amendment. As the Federal Circuit has previously written: “an amendment made to avoid prior art that contains the equivalent in question is not tangential.” Intervet Inc. v. Merial Ltd., 617 F.3d 1282 (Fed. Cir. 2010).
Thus, the non-infringement holding of Piramal stands.