Silvergate Pharms. Inc. v. Bionpharma Inc.

Epaned® (enalapril maleate)

April 29, 2021

GENERICally Speaking: A Hatch Waxman Litigation Bulletin

Case Name: Silvergate Pharms. Inc. v. Bionpharma Inc., No. 18-1962-LPS, 19-1067-LPS, 2021 WL 1751148 (D. Del. Apr. 29, 2021) (Stark, J.) 

Drug Product and Patent(s)-in-Suit: Epaned® (enalapril maleate); U.S. Patents Nos. 10,039,745 (“the ’745 patent”) and 10,153,987 (“the ’987 patent”)

Nature of Case and Issue(s) Presented: The patents-in-suit claimed enalapril formulations for the FDA-approved medication Epaned, which was an angiotensin converting enzyme (“ACE”) inhibitor used to treat hypertension and other cardiovascular conditions. After Bionpharma filed its ANDA seeking to make and sell a generic version of Epaned, Silvergate sued, alleging infringement of the patents-in-suit by the ANDA product under the doctrine of equivalents. Following a five-day bench trial, the court found that Bionpharma’s generic product did not infringe, on the basis of prosecution-history estoppel and the disclosure-dedication doctrine.

Why Bionpharma Prevailed: Two claim limitations were central to the issue of infringement under the doctrine of equivalents: the buffer limitation and preservative limitation. The buffer limitation required the presence of “a buffer comprising about 0.8 to about 3.5 mg/ml of citric acid and about 0.1 to about 0.8 mg/ml sodium citrate.” The ANDA product contained no citric acid and no sodium citrate. Silvergate argued that certain compounds in the generic product were equivalent to the claimed buffer, but this argument was rejected by the court. It found that under amendment-based prosecution-history estoppel, Silvergate was precluded from arguing that Bionpharma’s generic product infringed under the doctrine of equivalents. Specifically, the court found that during patent prosecution, Silvergate amended its claims in response to an obviousness rejection to include the limitation of “0.1 to about 0.8 mg/ml sodium citrate” and made clear to the Examiner that it was the specific concentrations of citric acid and sodium citrate that distinguished its invention from the prior art. As a narrowing amendment was presumed to be a surrender of all equivalents within the territory between the original claim and the amended claim, the court sided with Bionpharma’s argument that Silvergate sought to exclude formulations that did not contain sodium citrate at the requisite concentration, which included Bionpharma’s generic product. Armed with that finding, the court held that Silvergate failed to prove, by a preponderance of the evidence, that Bionpharma’s product contained a buffer equivalent to the claimed buffer.

The preservative limitation required “about 0.7 to about 1.2 mg/mL sodium benzoate.” Agains, Bionpharma’s generic product did not contain sodium benzoate. But Silvergate argued that it infringed under the doctrine of equivalents. The court rejected Silvergate’s argument in view of the disclosure-dedication doctrine, which foreclosed infringement theories concerning equivalents that are described in the patent specification but not claimed. The court found that Silvergate dedicated the embodiment in Bionpharma’s generic product to the public, and moreover, that a POSA could identify from the patent disclosure the alleged equivalent’s existence and suitability as an alternative to the claim sodium benzoate.

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