On appeal by Impax, the Federal Circuit affirmed the district court's decisions on enforceability and validity in light of one prior art patent. However, with respect to another prior art patent, the Federal Circuit vacated the finding of validity on the grounds that the district court had applied the wrong legal standard in assessing anticipation, and remanded the case for a reassessment using the proper legal standard. The Federal Circuit's discussion of the proper legal standard clarifies a subtlety of patent law: whether or not a prior art reference must be "effective" to be enabled.
The Federal Circuit distinguished the enablement standard under 35 U.S.C. 112 from that used to judge the sufficiency of allegedly anticipatory prior art references under 35 U.S.C. 102, and emphasized that the standard of enablement is indeed different between these two sections. The district court had judged an allegedly anticipating prior art reference not to anticipate because "there was no evidence that [what it taught] would be 'effective'" in practice. The Federal Circuit rejected this interpretation, stating, instead, that "proof of efficacy is not required for a prior art reference to be enabling for purposes of anticipation." Rather, to be anticipatory, a prior art reference must only "[describe] the claimed invention sufficiently to enable a person of ordinary skill in the art to carry out the invention".
An inconsistent standard of enablement is one of many subtleties in U.S. patent law. In Impax v. Aventis, the prior art references under consideration were U.S. patents, which carry with them a strong presumption of validity upon issue. One wonders if the Federal Circuit would have accorded equal treatment to non-patent prior art, all other facts being unchanged. The same "effectiveness" standard in 35 U.S.C. 112 and 102 would make the law easier for courts to apply, and either increase or decrease the probability of claims issuing, depending on which of the two standards were chosen. However, as far as the Federal Circuit is currently concerned, vive la différence.