Enalapril maleate – USA

Enalapril maleate – USA

On Apr. 27, 2021, Delaware court found Bionpharma’s product non-infringing under Doctrine of Equivalents (DOE).


Silvergate (Plaintiff) sued Bionpharma (Defendant) for infringement of US 9,669,008; US 9,808,442: US 10,039,745 and US 10,154,987 patents as Defendant filed ANDA under Hatch-Waxman Act. These patents are listed in Orange Book for the product, Epaned® (Enalapril maleate). Later, parties narrowed their disputes leaving only ‘745 and ‘987 patents. The Court held a five-day bench trial in February 2021. Silvergate concedes that Bionpharma does not literally infringe but infringes under the doctrine of equivalents (“DOE”). Bionpharma counters that prosecution history estoppel, disclosure-dedication, and claim vitiation – prevent Silvergate from prevailing on its DOE theories.

There were basically 2 infringement issues w.r.t. – a) buffer limitation & b) preservative limitation.


a) Buffer limitation – (“buffer comprising about 0.8 to about 3.5 mg/ml citric acid and about 0.1 to about 0.8 mg/ml sodium citrate”) :

Since, the court document was redacted, one could not identify actually what was there in Bionpharma’s product. But reading the entire decision, it was assumed that it does not contain buffer to maintain the pH. However, the product contains sodium hydroxide to provide specific pH to the solution. Anyway, Bionpharma argued that Silvergate is estopped from arguing DOE because of prosecution history estoppel. Specifically, Bionpharma  argued that during prosecution, Silvergate amended claims to include limitation of “0.1 to about 0.8 mg/ml sodium citrate”. Moreover, during prosecution when Examiner found claims obvious over certain prior arts, then Silvergate argued that the buffers specified in the claims are not taught in prior arts in the specific amount mentioned in the claims. These buffers are critical to the stability of the solution.


Court sided with Bionpharma & said that Silvergate made a narrowing amendment. Prior to amendment the claims required solely 1. 82 mg/mL of citric acid, while after amendment these same claims required both 1.82 mg/mL of citric acid and 0.15 mg/mL of sodium citrate dihydrate. Embodiments containing citric acid but not sodium citrate dihydrate would infringe the original claims but would not infringe the amended claims. Claim scope, therefore, was narrowed. Court next concluded that the amendment was made for the purposes of patentability. Here, Silvergate’s narrowing amendment was made in response to the Examiner’s obviousness rejections. Silvergate made clear that it was the specific concentration of citric acid and sodium citrate that distinguished its invention from the prior art. In repeatedly relating its unexpected stability results to the specific concentrations of specific ingredients in the amended claims, Silvergate necessarily made the identity and concentration of its ingredients central to overcoming the obviousness rejection. Court then with respect to surrendered material aspect, said that, Silvergate disclaimed all formulations not containing both 1.82 mg/mL of citric acid and 0.15 mg/mL of sodium citrate dihydrate.


Court further said that, even if Silvergate were not estopped from proceeding with its theory that Bionpharma’ s
ANDA Product infringes the buffer limitations under the doctrine of equivalents – which it is – the Court would find no infringement for the additional reason that Silvergate has failed to prove, by a preponderance of the evidence, that Bionpharma’s product contains a buffer equivalent to the buffer of the Asserted Claims.


b) Preservative limitation – (“about 0.7 to about 1.2 mg/mL sodium benzoate”) :

Court said that it is undisputed that the Bionpharma ANDA Product does not contain sodium benzoate. It has used different preservative (I assume it may be parabens). Bionpharma argued that its preservative cannot be found to infringe under the doctrine of equivalents because this embodiment was dedicated to the public under disclosure-dedication rule. Court said that the relevant inquiry is whether a POSA could identify, from the patent disclosure, the alleged equivalent’s existence and suitability as an alternative. Court further said that the preservative used in Bionpharma’s ANDA would be identified as an alternative to sodium benzoate based on patent disclosure. Therefore, Silvergate is precluded from arguing that Bionpharma’s preservative infringes under DOE.


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