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Infringement Under Doctrine of Equivalents Barred by Prosecution History Estoppel in CENESTIN Estrogen Therapy Case

Monday, August 1, 2011

Duramed Pharmaceuticals, Inc. v. Paddock Laboratories, Inc., No. 10-01419, 2011 BL 189841 (Fed. Cir. July 21, 2011) The U.S. Court of Appeals affirmed a district court's grant of summary judgment of noninfringement of an estrogen replacement drug patent, finding infringement under the doctrine of equivalents was barred by prosecution history estoppel. Moisture Barrier Coating Amendment Duramed Pharmaceuticals, Inc. ("Duramed") is the owner of U.S. Patent No. 5,908,638 (the '638 patent), relating to estrogen pharmaceutical compositions coated with a moisture barrier coating ("MBA") for use in hormone replacement therapies. During prosecution, Duramed overcame an obviousness rejection by amending claim 1 to limit the MBA to "ethylcellulose." Duramed markets its estrogen hormone replacement therapy product as CENESTIN. Paddock Laboratories, Inc. ("Paddock") filed an Abbreviated New Drug Application ("ANDA"), seeking FDA approval to market a generic version of CENESTIN. Paddock's proposed generic formulation, marketed as Opadry AMB, comprises a polyvinyl alcohol ("PVA") MBA instead of ethylcellulose. In response, Duramed brought suit in the U.S. District Court for the Southern District of New York against Paddock, alleging infringement of claims 1, 4, and 6-8 of the '638 patent under the doctrine of equivalents. Paddock moved for summary judgment of noninfringement, asserting that Duramed was barred by prosecution history estoppel from alleging that PVA met the ethylcellulose MBA limitation of the asserted claims. The district court granted Paddock's noninfringement summary judgment motion, finding that the amendment adding the ethylcellulose limitation was substantially related to patentability and narrowed the scope of the asserted claims, thus triggering the presumption of surrender for all equivalents under Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359 (Fed. Cir. 2003) (en banc). The district court also held that Duramed failed to rebut the Festo presumption, finding that use of PVA as a MBA in a pharmaceutical composition was foreseeable at the time of the amendment. Prosecution History Estoppel Bars Equivalence Infringement The Federal Circuit affirmed the noninfringement summary judgment, finding prosecution history estoppel barred Duramed from asserting infringement under the doctrine of equivalents. The court noted that since Duramed narrowed the scope of claim 1 in response to a prior art rejection, a presumption of prosecution history estoppel applied. Additionally, the Federal Circuit found that Duramed failed to rebut the presumption by showing that the alleged equivalent would have been unforeseeable at the time of the amendment. Rejecting Duramed's definition of the field of the invention restricting the suitability of PVA or Opadry AMB for use with conjugated estrogens, the Federal Circuit stated that when both original and issued claims begin "with the words '[a] pharmaceutical composition,' that language defines the field of the invention for purposes of determining foreseeability." Duramed at 7-8 (citing Schwarz Pharma, Inc. v. Paddock Labs., Inc., 504 F.3d 1371, 1377 (Fed. Cir. 2007)). Finding that an international patent application filed prior to the amendment pursuant to the Patent Cooperation Treaty ("PCT") disclosed formulations of PVA MBAs, including Opadry AMB, the Federal Circuit concluded that such PVA MBAs were known in the field of the invention, and, thus foreseeable. The Federal Circuit clarified that "even if the PCT disclosure indicates that PVA is less than ideal in some pharmaceutical uses as an MBC, it is still disclosed to be useful as such, and that renders it foreseeable for purposes of prosecution history estoppel. Foreseeability does not require flawless perfection to create an estoppel." Id. at 9. The court held that Duramed failed to rebut the presumption of prosecution history estoppel by showing that PVA MBCs would have been unforeseeable at the time of its narrowing amendment. Accordingly, the Federal Circuit affirmed the district court's grant of summary judgment of noninfringement.

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