In Purdue Pharma L.P. v. Endo Pharmaceuticals Inc., __ F.3d __ (Fed. Cir. 2006)(Plager, J.), a panel on rehearing vacated its earlier opinion, 410 F.3d 690 (Fed. Cir. 2005)(Plager, J.), and sent the case back to the trial court to reconsider the level of materiality of what it continued to consider Purdue's misrepresentation to the PTO, and also matters of scienter. This is one of the extremely rare situations where a panel of the court has granted rehearing in a case to reverse its earlier position.

The previous opinion had affirmed a trial court's finding that Purdue's OxyContin ® patent is unenforceable due to inequitable conduct where Purdue had made representations of unexpected results to the Examiner based upon "insight" and not hard experimental evidence – and where Purdue did not explain this to the Examiner.

The court found "Purdue's actions [meet] a threshold level of materiality"; even though "[t]his omission of information was material, [it was] not as material as an affirmative misrepresentation would have been." (citation omitted). Remand was necessary, because "the trial court may have erred to the extent it relied on a high level of materiality in determining whether Purdue intended to deceive the PTO and whether Purdue ultimately committed inequitable conduct." Mistakes were also found in the trial court's determination of scienter.

On remand, "the trial court should rethink the relevance of the evidence relating to whether Purdue could prove that OxyContin ® was the most easily titratable analgesic. If the trial court still finds that a threshold level of intent to deceive has been established, the court should reweigh its materiality and intent findings to determine whether the sanction of unenforceability due to inequitable conduct is warranted. In making this determination, the trial court should keep in mind that when the level of materiality is relatively low, the showing of intent must be proportionately higher."