In Duramed Pharmaceuticals, Inc. v. Paddock Laboratories, Inc., the Federal Circuit rejected Duramed’s arguments that prosecution history estoppel did not bar application of the doctrine of equivalents under Festo because the equivalent at issue was not foreseeable. In so doing, the Court illuminated the rather narrow applicability of the “unforeseeable” route to rebutting a presumption of prosecution history estoppel.

The Patent At Issue

The patent at issue was Duramed’s U.S. 5,908,638, directed to pharmaceutical compositions of conjugated estrogens. The only independent claim is claim 1:

1. A pharmaceutical composition in a solid, unit dosage form capable of oral administration for the hormonal treatment of peri-menopausal, menopausal and post-menopausal disorders in a woman comprising:
conjugated estrogens coated onto one or more organic excipients forming a powdered conjugated estrogen composition where said composition is substantially free of inorganic excipients and further comprises about 30-70% gel-forming organic excipient and about 30-70% non-gel forming organic excipient by weight and having less than about 2.5% free water by weight and greater than 2.5% total water wherein said solid unit dosage form is coated with a moisture barrier coating comprising ethylcellulose.

The claimed invention is said to address the water-sensitivity of conjugated estrogens by providing a “moisture barrier coating” (MBC). While the original claims recited an MBC generally, the highlighted phrase reciting ethylcellulose was added during prosecution to overcome an obviousness rejection.

The Accused Product

Paddock filed an Abbreviated New Drug Application (ANDA) seeking to launch a generic version of Duramed’s Cenestin® product. Instead of an ethylcellulose MBC, Paddock’s product uses a polyvinyl alcohol (sold commercially as Opadry AMB) for its MBC.

The Infringement Dispute

Duramed alleged infringement under the doctrine of equivalents, asserting that Paddock’s polyvinyl alcohol (PVA) MBC was equivalent to the claimed ethylcellulose MBC.

Paddock asserted that prosecution history estoppel applied, citing the claim amendment that defined the MBC as comprising “ethylcellulose.” Paddock also cite pre-amendment (but not prior art) references alleged to show that PVA-based MBCs were known in the art at the time the amendment was made.

The district court agreed with Paddock and granted Paddock’s motion for summary judgment of noninfringement.

The Federal Circuit’s Analysis

The Federal Circuit decision includes a succinct summary of the doctrine of equivalents and its limitation by the doctrine of prosecution history estoppel, with citations to the 2002 Supreme Court decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.:

Under the doctrine of the 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.” . . . However, the doctrine of prosecution history estoppel prevents a patent owner from recapturing through the doctrine of equivalents subject matter surrendered to acquire the patent.

As the Federal Circuit explained, “[b]ecause . . . Duramed narrowed the scope of the ’638 patent’s claims in response to a prior art rejection, a presumption of prosecution history estoppel applies.” However, “Duramed may rebut that presumption by showing, inter alia, the ‘alleged equivalent would have been “unforeseeable at the time of the amendment and thus beyond a fair interpretation of what was surrendered.”‘ Citing Festo, the Federal Circuit noted: 

[A]n alternative is foreseeable if it is disclosed in the pertinent prior art in the field of the invention. In other words, an alternative is foreseeable if it is known in the field of the invention as reflected in the claim scope before amendment.

Applying this principle here, the Federal Circuit upheld the district court decision.

The Federal Circuit rejected Duramed’s argument that the references cited by Paddock were too far afield, because they did not teach the use of Opadry AMB for moisture-sensitive pharmaceutical compounds. Instead, the Federal Circuit noted that the preamble of the claims—”a pharmaceutical composition”—”defines the field of the invention for purposes of determining foreseeability.” Because Paddock had shown that PVA MBCs were known for use in pharmaceutical compositions at the time of Duramed’s amendment, they were a “foreseeable” alternative surrendered by the amendment.

The Federal Circuit also rejected Duramed’s arguments that the cited references did not demonstrate the suitability of PVA as an MBC, stating that “foreseeability does not require . . . precise evidence of suitability.”

Seeing Through The Fog

This case underscores the difficulty of asserting the doctrine of equivalents when the claim limitation at issue was amended during prosecution, and the particular difficulty of establishing that the equivalent at issue was unforeseeable.

The timeframe of the foreseeability inquiry is interesting and important. Because foreseeability is assessed as of the time of the amendment—not as of the filing date or priority date—references that are not prior art can be relevant. That is, post-filing date, later-developed equivalents can be surrendered during prosecution as long as the equivalents were known by the time the claims were amended.

The scope of relevant references—and the impact of the preamble—also are interesting and important. It is a common practice to claim “[a] pharmaceutical composition …” comprising a particular drug, even when the composition is specifically developed and tailored to the particular drug. This case may provide a reason to write the preamble more narrowly (“a pharmaceutical conjugated estrogen composition …”?), although it is not clear that having a narrower preamble would have affected the outcome here.