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Stretching Claim Scope through the Doctrine of Equivalents

In a decision that could make enforcement capabilities a little bit broader for patent owners, especially in drug delivery, the Federal Circuit recently affirmed a decision finding infringement under the doctrine of equivalents.

As part of this decision in UCB, Inc. v. Watson Laboratories Inc., the appeals court considered infringement of a patent on a transdermal therapeutic system for treating Parkinson’s syndrome. In particular, the claims recited “an acrylate-based or silicone-based polymer adhesive system.” The parties agreed that the accused infringer’s patch met all other claim limitations, but the patch had a polyisobutylene-based adhesive (PIB adhesive) instead of the acrylate-based or silicone-based adhesives. The trial court found that the defendant’s patch infringed the claims anyway, applying the doctrine of equivalents.

To affirm the district court, the Federal Circuit first considered (a) prosecution history estoppel, (b) intentional narrow claiming, (c) vitiation, and (d) ensnarement, any of which would have blocked the doctrine of equivalents. For each concept, the Federal Circuit found that the patent owner was in the clear, giving a helpful summary of the limits on the doctrine of equivalents in the process.

Prosecution history estoppel prevents the doctrine of equivalents from covering claim scope that the patent owner gave up during prosecution. Here, the accused infringer tried to argue that a response to a restriction requirement prevented coverage of PIB adhesives as equivalents. However, restriction responses do not necessarily trigger estoppel. The court noted here that the Examiner’s distinction between the groups of claims was based on the need for a solubility enhancer in the other claims, not on the polymer adhesive itself, and that the patent owner never introduced any limitation in the claims excluding polyisobutylene.

Intentional narrow claiming, the defendant argued, would have prevented the patent owner from asserting the claims against a broader scope that they could have covered literally. However, the Federal Circuit cited earlier decisions to state that “foreseeability” of different claim scope does not prevent the use of the doctrine of equivalents. The Federal Circuit also distinguished this case over other cases, finding that the PIB adhesive in this context was perhaps not so foreseeable as the defendant would have liked.

Vitiation prevents the doctrine of equivalents from removing any meaning or effect of a claim limitation. The Federal Circuit found that the equivalence of PIB adhesives would not mean that the claims could cover just any adhesive, and therefore that the claim limitation would still have meaning even if covering PIB adhesives.

Ensnarement prevents the doctrine of equivalents from covering anything which was already in the prior art. However, in this case, the court found the defendant’s ensnarement arguments added nothing to their case for invalidity of the claims as requiring an acrylate-based or silicone-based polymer adhesive system. The court therefore addressed the defendant’s validity arguments in a separate section.

Then, the Federal Circuit looked to the main arguments about equivalents, considering whether the differences between the PIB adhesive and the acrylate- or silicone-based adhesives would have been substantial or not. The court noted that all of these adhesives are pressure-sensitive, biologically inert, non-irritating, and non-toxic. The court acknowledged the differences in chemical structure between PIB and polymers containing functional groups like acylate- or silicone-based polymers, along with the resulting differences in polarity, reactivity, adhesiveness, and crosslinking potential. However, in this specific context of transdermal drug delivery, the district court had found that these differences were not substantial.

When handling the doctrine of equivalents, the Supreme Court has noted, somewhat confusingly, that “[d]ifferent linguistic frameworks may be more suitable to different cases, depending on their particular facts.” The Federal Circuit has similarly discussed the doctrine of equivalents as “simple to articulate” but “conceptually difficult to apply.” This can make analysis under the doctrine of equivalents difficult, magnifying the importance of understanding cases like this one.

myersEric Myers