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The Court of Appeals for the Federal Circuit this week affirmed a district court's finding that prosecution history estoppel barred a pharmaceutical manufacturer's allegations of infringement under the doctrine of equivalents.
The plaintiff, Duramed Pharmaceuticals, claimed a patent for conjugated estrogen pharmaceutical compositions for use in a hormone replacement therapy it produces. Because conjugated estrogens are extremely water sensitive and susceptible to moisture degradation in storage, Duramed developed a conjugated estrogen formula that included a moisture barrier coating (MBC) to inhibit the drug's moisture absorption and reduce storage-related degradation.
Duramed filed a patent application on its formulation in July 1995.
After initially rejecting Duramed's patent application for a compound "coated with a moisture barrier coating" that "comprises ethylcellulose" as obvious, the patent examiner advised that he would allow the application with an amendment. Duramed amended the application to recite pharmaceutical compositions with "a moisture barrier coating comprising ethylcellulose," and received the patent on December 3, 1998.
In March 2009, Duramed filed suit against Paddock Laboratories alleging infringement of its patent based on Paddock's Abbreviated New Drug Application for a generic version of Cenestin, Duramed's hormone replacement therapy drug. Duramed alleged infringement under the doctrine of equivalents because Paddock's proposed generic product uses a polyvinyl alcohol (PVA) MBC marketed as Opadry AMB.
Paddock moved for summary judgment, arguing that Duramed's claim was barred by amendment-based prosecution history estoppel. Paddock relied on several pre-amendment references, including an international patent application filed by Colorcon pursuant to the Patent Cooperation Treaty (PCT). The Colorcon PCT, published in January 1996, discloses formulations of PVA-MBCs for use with pharmaceutical compositions. The Colorcon PCT then, in the "Summary of the Invention," discloses preferred PVA grades and identifies a plasticizer that does not compromise PVA's properties as a moisture barrier.
Duramed narrowed the scope of its patent's claims in response to a prior art rejection, so a presumption of prosecution history estoppel applied. The court found that Duramed failed to rebut the presumption of prosecution history estoppel based on unforeseeability. The court noted that PVA MBCs needed only to have been known in the field of pharmaceutical compositions as of the time of Duramed's narrowing amendment to its application. The Colorcon PCT disclosed the use of PVA as MBCs in the field of pharmaceutical compounds prior to December 3, 1998, rendering such PVA MBCs foreseeable at the time of Duramed's narrowing amendment.