As we previously reported (here), the U.S. District Court for the Northern District of Illinois in an August 2017 decision in Oil Dri Corp. v. Nestle Purina Petcare Co., No. 1-15-cv-01067 (N.D. Ill., Aug. 2, 2017) joined the seeming trend of courts interpreting estoppel against patent challengers in inter partes review (IPR) proceedings more broadly than previously had been the case.  According to this broader view, the prohibition provided in 35 U.S.C. § 315(e)(2) against asserting in litigation invalidity grounds that the petitioner “reasonably could have raised during” an IPR is not limited to grounds litigated in the IPR trial phase but covers grounds that could have been raised in the IPR petition had the petitioner been reasonably diligent.  Applying this interpretation, the Court found that estoppel barred the assertion of four of seven patent references that the Court concluded a “skilled searcher conducting a diligent search reasonably could have been expected” to discover.  It reserved its decision on the three remaining references pending further argument.

Now, the Court has issued its opinion on those remaining references, finding that they, too, cannot be asserted in the pending district court litigation because they were shown to be in the IPR petitioner (Purina)’s possession prior to the filing of the IPR petition and therefore “reasonably could have been raised” in the IPR petition.  Despite an intervening decision of another district court that bucked the trend toward broader interpretation of the IPR-estoppel statute (Koninklijke Philips N.V. And Philips Lighting North America Corp., v. Wangs Alliance Corp., No.  1-14-cv-12298-DJC (D. Mass., Jan. 2, 2018) (discussed in a prior post)), the Illinois court doubled down on its view that “the purpose of IPR proceedings” as “an efficient alternative to litigation” justified its approach to IPR estoppel; and, citing a Wisconsin decision, it added that a party who challenged a patent’s validity in an IPR should not be allowed to hold some references “‘in reserve for a second bite at the invalidity apple.’”