Federal Circuit Finds Prosecution History Estoppel Prevents Coverage of Equivalent Since Amendment Was Foreeseable Equivalent

In Duramed Pharmaceuticals, Inc v Paddock Labritories, Inc., 644 F3d 1376, 99 USPQ2d 1388 (Fed. Cir. 2011), Duramed (now known as Teva Women’s Health Inc.) owns U.S. Patent No. 5,908,638 (‘638 patent.), which is directed to estrogen pharmaceutical compositions.  When originally filed, original independent claim 1 recited a conjugated estrogen pharmaceutical composition “coated with a moisture barrier coating,” and original dependent claim 7 limited “said moisture barrier coating” to one that “comprises ethylcellulose.”  During prosecution, the examiner rejected both claims for obviousness.  However, after an interview, the Examiner indicated that if the limitation of claim 7 was included the independent claim 1, it would be allowed. Duramed amended claim 1 to include the limitation, and the claim was allowed.  Thus, claim 1 of the issued ‘638 patent claimed pharmaceutical compositions for hormonal treatment of pre-menopausal, post-menopausal, and menopausal disorders with “a moisture barrier coating comprising ethylcellulose.”

In 2009, Duramed brought suit against Paddock under 35 U.S.C. §271(e)(2) for infringement of  the ‘638 patent. Paddock had proposed in an Accelerated New Drug Application for a generic version of Duramed’s hormone replacement utilizing polyvinyl alcohol (PVA) for a moisture barrier coating (marketed as Opadry AMB.)  Duramed asserted that the generic version infringed claims 1, 4, and 6-8 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 of noninfringement, arguing that Duramed was barred by amendment-based prosecution.

The district court granted summery judgment of non-infringement to Paddock since these equivalents were known in the prior art at the time of the amendment and were thus foreseeable.  The district court held that the prosecution history estopped Duramed from infringement allegations, because the amendment narrowed the scope of the claim triggering the presumption under Festo that Duramed had surrendered all territory between the original and amended claim scope. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359 (Fed. Cir. 2003). Further, the district court held that the Duramed Failed to rebut the Festo presumption based on an argument of, inter alia, the foreseeablity of the use of PVA as a MBC in a pharmaceutical formulation.  Specifically, the district court found foreseeability based upon: 1) a PCT to Colorcon published January 25, 1996 that disclosed formulations of the PAV based MBC, including Opadry AMB which included technical drawbacks, 2) U.S. Patent No. 3,935,326 to Groppenbacher issued in 1976 that discloses the use of PVA in moisture tight tablets, 3) an article in 1995 of “Manufacturing Chemist” that tested Opadry AMB and concluded that it was a highly effective moisture barrier, 4) scientific articles on PVA MBC distributed conferences in May 1995, May 1998, and November 1998, and 5) invoices from Colorcon indicating sales of Opadry AMB before September of 1996.

On appeal, the Federal Circuit noted that, under the doctrine of equivalents, “a product or process that does not literally infringe the express terms of a patent claim may nonetheless be found to infringe if there is ‘equivalence’ between the elements of the accused product or process and the claimed elements of the patented invention.” Warner-Jenkins Co. v. Hilton Davis Chem. Co., 520 U.S. 17 (1997) (citing Graver Tank & Mfg. Co. v Linde Air Prods. Co., 339U.S. 605 (1950)). However, the doctrine of prosecution history estoppel prevents these equivalents from reaching subject matter surrendered to acquire the patent. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 734 (2002).  The presumption is rebuttable if at the time of the amendment the alleged equivalents would not have been foreseeable and thus beyond the fair interpretation of what was surrendered. An alternative is foreseeable if it is known in the field of invention as reflected in the claim prior to amendment.  Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359, 1366-67 (Fed. Cir. 2003) (en banc)

Duramed argued that this interpretation of foreseeablity would mean that any mention of the alleged equivalent in the prior art would make it equivalent as a matter of law. Instead Duramed argued that an equivalent was not foreseeable if it is not understood by one of ordinary skill in the art to be suitable for use in the invention that was originally claimed. Specifically, they argued that PVA was not disclosed as a suitable MBC for moisture sensitive pharmaceuticals such as conjugated estrogen.

Padock responded that the foreseeablity standard only requires that PVA be a foreseeable MBC for pharmaceutical applications at the time of the narrowing amendment. The Colorcon PCT would be suffiecent to render PVA foreseeable, but it is also bolstered by the Groppenbacher patent, scientific publishings, and the commercialization of Opadry.

The Federal Circuit held that Duramed had failed to rebut the presumption of prosecution history estoppel based on unforseablity. The court also noted that Duramed’s overly restrictive definition of the field of invention. Specifically in Schwarz, the court had previously held that if the original and issued claims start with language such as “[a] pharmaceutical composition” it defines the field of invention for the purposes of foreseeability. Schwarz Pharma, Inc. v. Paddock Labs., 504 F.3d 1371 (Fed Cir. 2007). At the time of the narrowing amendment of the Duramed claim, PVA MBCs need only to have been known in the field of pharmaceutical compositions, the Colorcon PCT establishes this.

Although, the Colorcon PCT gives only conclusory statements, list drawbacks, and lacks data on the stability of pharmaceutical compounds, foreseeablity does not require such precision evidence of suitability. Disclosure that the equivalent would be useful as such would be sufficient to render it foreseeable for the purposes of prosecution estoppel. “Foreseeablity does not require a flawless perfection to create estoppel.”  As such, the Federal Circuit upheld the district court’s grant of summary judgment of noninfringement.

Significance to Patent Applicants

Duramed is an important reminder that, while the doctrine of equivalents is available, it is very difficult to apply where the equivalence is for an element added through amendment during prosecution.  While technically possible to overcome, such amendments will generally bar any equivalence except in all but the most inconsequential changes.  As demonstrated in Duramed, this is because foreseeability is not limited to what was foreseeable by the inventors (and thus disclosed in the specification), but from anything accessible to one skilled in the art.  Therefore, while tempting, applicants need to be careful in amending claims simply to obtain a quick allowance since doing so often has unforeseen consequences.


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