The Federal Circuit has affirmed infringement under the doctrine of equivalents in a number of cases over the last few years. Briefly, the judicially created doctrine of equivalents is intended to expose those who adopt the essence of the invention while avoiding the literal language of a patent claim to liability for infringement. In other words, even though a product does not literally possess each and every element of a claim, a patent owner can pursue an infringement claim if the accused product and the patented product are substantial equivalents of each other.

However, there are limits to the application of the doctrine of equivalents. For example, when the alleged equivalent was disclosed but not claimed in the specification, thus considered to be dedicated to the public (otherwise known as the dedication-disclosure rule) or the alleged equivalent was surrendered during prosecution to obtain allowance (otherwise known as prosecution history estoppel), infringement under the doctrine of equivalents is unavailable to a patent owner. And, if applicable, these limitations provide an opportunity for an accused infringer to bring an infringement suit to a relatively quick conclusion. Indeed, as evidenced by the Federal Circuit’s recent decision in Eagle Pharmaceuticals Inc. v. Slayback Pharma LLC, the dedication-disclosure rule allowed an accused infringer to obtain judgment of non-infringement on the pleadings alone.

By way of background, Eagle Pharmaceuticals, Inc. brought suit against Slayback Pharma LLC in the District of Delaware in late 2018 alleging infringement of four patents related to Eagle’s bendamustine product BELRAPZO^®. Since Slayback’s generic bendamustine product did not literally include a “pharmaceutically acceptable fluid,” as required by the asserted claims, Eagle’s infringement position was based on the doctrine of equivalents. More specifically, the claims required that the pharmaceutically acceptable fluid include “a mixture of polyethylene glycol and propylene glycol, wherein the ratio of polyethylene glycol to propylene glycol in the pharmaceutically acceptable fluid is from about 95:5 to about 50:50,” but Slayback’s generic product employed ethanol rather than propylene glycol. Since the specification of the asserted patents repeatedly identified ethanol as an alternative to propylene glycol but the claims did not, Slayback quickly moved for an early judgment of noninfringement on the pleadings under Rule 12(c) based on the dedication-disclosure rule. In opposition, Eagle argued that the specification of the asserted patents did not disclose ethanol as an alternative for the specific antioxidant bendamustine formulation featured in the claims. In fact, Eagle submitted unrebutted expert testimony to that effect. Much to Eagle’s dismay, five months after Eagle filed its complaint, the district court judge decided the motion in Slayback’s favor without considering the proffered expert testimony.

On appeal, Eagle argued that the district court erred in its determination on the merits that the disclosure-dedication rule applied and also procedurally erred by ignoring the factual dispute that purportedly existed, i.e., whether a person of ordinary skill in the art would have understood the specification to disclose ethanol as an alternative to propylene glycol for the claimed invention. The court did not find either challenge persuasive and affirmed the district court’s judgment. 

In doing so, the court first explained that, for the dedication-disclosure rule to bar application of the doctrine of equivalents, the specification must clearly disclose — but not claim — the alleged equivalent at issue. While Eagle continued to argue that the specification did not suggest ethanol as an alternative for the claimed antioxidant formulation, the court rejected this embodiment-level approach. Indeed, the specification does not have to match the claimed embodiment exactly for the dedication-disclosure rule to apply. Rather, the dedication-disclosure rule merely requires that the specification disclose the unclaimed alleged equivalent as an alternative to the relevant claim limitation. In this aspect, the court found that the specification had numerous teachings to use ethanol as the pharmaceutically acceptable fluid (and did not suggest that ethanol was limited to use in only the unclaimed chloride salt formulation, as argued by Eagle).

As to the procedural challenge, the Federal Circuit agreed with Eagle that, for a Rule 12(c) judgment to be appropriate, there must be no material issues of fact. However, the court was not persuaded by Eagle’s argument that the lower court was required to infer that the person of ordinary skill in the art would not have comprehended that ethanol was an alternative to propylene glycol or that the expert testimony was improperly ignored. Since district courts have discretion to consider evidence outside the complaint when ruling on a Rule 12(c) motion, the Federal Circuit found no error in the lower court’s treatment of the expert testimony proffered by Eagle. Ultimately, the court concluded that “the only reasonable inference that can be made . . . is that a skilled artisan would understand the patents to disclose ethanol as an alternative to the claimed propylene glycol.” 

In short, Slayback was able to avoid protracted litigation related to Eagle’s infringement claim because Eagle’s specification included unclaimed subject matter that formed the basis for the infringement allegation under the doctrine of equivalents. Similarly, prosecution history estoppel has also proved to be an effective tool that may be used as an affirmative defense early in litigation. In fact, last summer, the Federal Circuit affirmed the lower court’s dismissal of Amgen’s complaint for failure to state a claim in Amgen Inc. v. Coherus Biosciences Inc. based on prosecution history estoppel. Amgen, who had alleged infringement under the doctrine of equivalents, clearly and unmistakably surrendered the alleged equivalents during prosecution of the asserted patent. Accordingly, the court determined that the lower court’s “[p]rosecution history estoppel thus bars Amgen from succeeding on its infringement claim under the doctrine of equivalents.”

The main takeaway: It is not too early to apply the countervailing doctrines of the dedication-disclosure rule and prosecution history estoppel at the Rule 12 stage of litigation, so seize the opportunity to potentially bring a speedy end to the dispute.