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Disclosure of a Less-Than-Ideal Use of a Prior Art Compound Is Sufficient to Render It Foreseeable for Purposes of Prosecution History Estoppel

July 21, 2011

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Last Month at the Federal Circuit - August 2011

Judges: Lourie (author), Gajarsa, Dyk

[Appealed from: S.D.N.Y., Senior Judge Sand]

In Duramed Pharmaceuticals, Inc. v. Paddock Laboratories, Inc., No. 10-1419 (Fed. Cir. July 21, 2011), the Federal Circuit affirmed the district court’s grant of SJ of noninfringement, finding that prosecution history estoppel barred Duramed Pharmaceuticals, Inc.’s (“Duramed”) allegations of infringement under the DOE.

Duramed owns U.S. Patent No. 5,908,638 (“the ’638 patent”), which claims conjugated estrogen pharmaceutical compositions for use in hormone replacement therapies. The conjugated estrogens are extremely water sensitive and highly susceptible to moisture degradation during storage. To counteract those limitations, Duramed developed a formulation that included a moisture barrier coating (“MBC”).

Claim 1 of the original ’638 patent application recited a conjugated estrogen pharmaceutical composition “coated with a moisture barrier coating.” Claim 7 limited the coating to one that “comprises ethylcellulose.” During prosecution, the examiner rejected the claims as obvious, but advised that the application would be allowed if Duramed amended claim 1 to include, inter alia, the ethylcellulose limitation of claim 7. Duramed complied, and amended claim 1 thus recited, “A pharmaceutical composition in a solid, unit dosage form . . . comprising: conjugated estrogens . . . wherein said solid unit dosage form is coated with a moisture barrier coating comprising ethylcellulose.”

Duramed sued Paddock Laboratories, Inc. (“Paddock”) for infringement of the ’638 patent based on Paddock’s ANDA for a generic version of Duramed’s hormone replacement therapy product, Cenestin®. Duramed alleged infringement under the DOE because Paddock’s proposed generic product used a polyvinyl alcohol (“PVA”) MBC marketed as Opadry AMB, and not an ethylcellulose MBC.

Paddock moved for SJ of noninfringement, arguing that Duramed was barred by amendment-based prosecution history estoppel from alleging that PVA was equivalent to ethylcellulose in the MBC limitation of the asserted patent claims. The district court granted Paddock’s motion, finding that (1) Duramed’s amendment was substantially related to patentability and, because it narrowed the scope of the asserted claims, it triggered the presumption under Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359, 1366-67 (Fed. Cir. 2003) (en banc), that Duramed surrendered all territory between the original and amended claim scope; and (2) Duramed’s argument—that the use of PVA as an MBC in a pharmaceutical formulation was unforeseeable at the time of the amendment—did not rebut the Festo presumption.

On appeal, Duramed argued that the district court applied the wrong legal test for foreseeability because the district court held that any mention of an alleged equivalent in the prior art makes that equivalent foreseeable as a matter of law. Instead, Duramed asserted that an equivalent is not foreseeable if it was not understood by one of ordinary skill in the art to be suitable for use in the invention as originally claimed. As applied here, Duramed alleged that the relevant art did not disclose either PVA or Opadry AMB as suitable MBCs for moisture-sensitive pharmaceutical compounds similar to conjugated estrogens.

The Federal Circuit agreed with the district court that Duramed failed to rebut the presumption of prosecution history estoppel on the basis of unforeseeability. First, the Court found that Duramed’s narrowing amendment in response to a prior art rejection triggered the Festo presumption. Second, the Court rejected Duramed’s attempt to unduly narrow the field of invention and consequently limit the prior art that could lead to a conclusion of foreseeability. The Court noted that “an alternative is foreseeable if it is known in the field of invention as reflected in the claim scope before amendment.” Slip op. at 6 (quoting Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 493 F.3d 1368, 1379 (Fed. Cir. 2007)).

As applied here, the Federal Circuit reiterated that when the language of both the original and issued claims “begins with the words ‘[a] pharmaceutical composition,’ that language defines the field of the invention for purposes of determining foreseeability.” Id. at 7-8 (alteration in original) (citing Schwarz Pharma, Inc. v. Paddock Labs., Inc., 504 F.3d 1371, 1377 (Fed. Cir. 2007)). Further, the prior art established that PVA MBCs were known in the field of pharmaceutical compositions at the time of Duramed’s amendment. The Court rejected Duramed’s arguments that the prior art failed to establish that PVA-based Opadry AMB was suitable as an MBC because the prior art reference provided only conclusory statements and lacked any data on the stability of the pharmaceutical compounds coated with Opadry AMB, finding instead that “foreseeability does not require such precise evidence of suitability.” Id. at 9.

The Court noted that even if PVA was disclosed as 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. Thus, Duramed failed to overcome the Festo presumption on the basis of unforeseeability because the prior art disclosed the use of PVA as an MBC in the field of pharmaceutical compounds prior to Duramed’s amendment.

Summary authored by Derrick L. Wang, former summer intern at Finnegan.