Case Name: Astellas Pharma Inc. v. Zydus, Inc., Civ. No. 20-1589, 2025 WL 1111447 (D. Del. Apr. 15, 2025) (Bataillon, J.)
Drug Product and Patent(s)-in-Suit: Myrbetriq® (mirabegron); U.S. Pat. No. 10,842,780 (“the ’780 patent”)
Nature of the Case and Issue(s) Presented: Myrbetriq is a drug used to treat overactive bladder. It utilizes a hydrogel-based sustained-release oral tablet formulation to control the rate at which the active ingredient, mirabegron, is released into the bloodstream over time. The ’780 patent claims a sustained-release pharmaceutical compositions of mirabegron comprising a hydrogel-forming polymer and a water-soluble additive. The claims include functional limitations regarding specific dissolution profiles related to dissolution rates. The claimed formulations consist of three essential components: (i) mirabegron; (ii) a hydrogel-forming polymer that swells upon contact with gastric fluids; and (iii) a water-soluble additive that facilitates fluid penetration. These sustained-release characteristics allow for maintaining consistent therapeutic levels while mitigating side effects.
Astellas sued Zydus and Lupin after the generic manufacturers filed ANDAs with the FDA seeking to make and sell generic mirabegron. The lawsuit focused on the validity of the ’780 patent. After a remand from the Federal Circuit, the district court was asked to resolve three key issues: (i) whether the patent was enabled; (ii) whether the patent satisfied the written description requirement; and (iii) whether the claims were indefinite under 35 U.S.C. § 112. The court found in favor of Astellas.
Why Astellas Prevailed: The court held that the ’780 patent was enabled because a POSA could practice the full scope of the claimed invention using routine, well-understood experimentation. Specifically, the court held that although practicing the invention requires making candidate formulations and performing dissolution testing—it did not require trial and error testing, and any testing required is “‘routine’ and helped along by the ‘reasonable amount of guidance regarding the direction of experimentation’ provided by the specification.” Second, the court rejected Defendants’ written description challenge. Although the claims recite a genus of hydrogel-based formulations, the patent disclosed sufficient representative species and provided a detailed explanation of how the claimed formulations functioned. It included multiple working examples with specific compositions and dissolution data showing performance consistent with the claimed functional limitations. Finally, the court concluded the claims were not indefinite. The generic manufacturers had argued that the patent failed to specify when dissolution testing should occur. The court disagreed, explaining that the patent instructed testing using standard USP protocols, and a POSA would understand to use unexpired, representative samples.
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