Narrowing a Patent Claim Can Prove

Costly During Litigation — and a Broadly

Worded Preamble Doesn’t Help

 

By Nancy C. Wilker, a member of our Life Sciences Practice Group

 

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n case patent prosecutors needed reminding that the art of claim drafting is much akin to fortune telling, a recent case by the Federal Circuit throws the spotlight on the preamble - the formal introductory clause of a claim - and its role in the doctrine of equivalents.

The patent claims at issue in Duramed Pharmaceuticals v. Paddock Laboratories pertain to a moisture barrier coating for use with an estrogen formulation therapy. Estrogen formulations, which are used clinically to relieve menopausal symptoms, are extremely water-sensitive, and thus are amenable to a moisture barrier coating to prolong shelf-life and stability.

During prosecution, to overcome an obviousness rejection, Duramed amended its claim to require that the moisture barrier coating comprise ethylcellulose. Duramed was issued U.S. Patent No. 5,908,638. The preamble to the claim at issue read: “A pharmaceutical composition . . . comprising:” and the claim ended with, “wherein said solid unit dosage form is coated with a moisture barrier coating comprising ethylcellulose.”

When Paddock Laboratories filed an Abbreviated New Drug Application for a generic estrogen formulation which used a moisture barrier coating comprising polyvinyl alcohol, Duramed sued for infringement of the ‘638 patent under the doctrine of equivalents. This doctrine comes to the rescue of a patent owner when an accused product does not literally infringe, but an equivalence is found between its elements and the claimed elements of the patented invention.

But the countervailing doctrine of prosecution history estoppel, which the Supreme Court explicated in its high-impact 2002 decision in Festo Corp. v. Shoketsu, also comes into play: If a narrowing claim amendment is made during patent prosecution, the surrendered claim scope is presumed to be stripped of equivalents if those equivalents were foreseeable in the field of the invention.

Predictably, then, Paddock defended by asserting that Duramed had surrendered the claim scope for the moisture barrier coating with its amendment requiring that the coating comprise ethylcellulose. Just as predictably, Duramed responded that the use of polyvinyl alcohol as a moisture barrier coating was unforeseeable at the time of the amendment and therefore not surrendered.

The Federal Circuit found for Paddock, stating that Duramed had indeed surrendered the use of polyvinyl alcohol as a moisture barrier coating because its use had been known at the time the amendment was made. Although the art describing the use of polyvinyl alcohol as a moisture barrier coating recognized its several drawbacks, the court held that its use was still foreseeable for purposes of barring Duramed’s infringement claim since “foreseeability does not require flawless perfection to create an estoppel.”

The court laid significance on the preamble to Duramed’s patent claim. The words, “a pharmaceutical composition comprising. . .,” were held to define the field of the invention when determining whether a particular ingredient would be a “foreseeable” alternative to the moisture-barrier layer that Duramed claimed.

The art, which described polyvinyl alcohol as a moisture barrier coating “for pharmaceutical tablets and the like,” was found to be applicable to the ‘638 claims even though the art made no mention of estrogen formulation. Duramed could have included that ingredient in its claim but did not.

In recent years, the courts have stressed that it would be unjust to let a patentee use the doctrine of equivalents to recapture patent territory that had been voluntarily surrendered in order to acquire the patent.

Consistent with this outlook, Duramed tells us that, when you amend a claim in order to gain its allowance, any litigation argument that the accused infringer’s equivalent is unforeseeable is highly unlikely to be persuasive. And broad language in a claim’s preamble has the potential to magnify the effect of prosecution history estoppel.