Recently, the Federal Circuit affirmed a decision from the United States Patent and Trademark Office Patent Trial and Appeal Board (“the Board”) finding claims of Purdue’s latest abuse deterrent, extended release oxycodone patent, U.S. Patent No. 9,034,376 (“the ’376 patent”), obvious over reference combinations including Pub. No. US 2002/0187192 A1 (“Joshi”).  Purdue Pharma L.P., et al. v. Iancu, 2019 U.S. App. LEXIS 11205 (Fed. Cir. 2019).  In its decision, the Court held that collateral estoppel did not apply to issues that could have been raised in a prior litigation.

The Board found that Purdue was collaterally estopped from challenging Joshi’s availability as prior art because Purdue had not raised the issue in a previous district court litigation involving U.S. Patent No. 8,337,888 (“the ’888 patent”), which claims priority to the same provisional application as the ’376 patent at issue.  In the ’888 patent litigation, the district court invalidated the claims as obvious based on combinations that included Joshi.

On appeal of the Board’s invalidity ruling in the IPR of the ’376 patent, the generic defendants argued that collateral estoppel applies because Purdue, by not distinguishing between Joshi’s provisional and non-provisional applications in the ’888 patent litigation, implicitly admitted that the disclosures in Joshi and its provisional application were interchangeable.  Appellees also argued that during the ’888 patent litigation Purdue addressed the relevant teachings of Joshi and its provisional application, but never directly challenged the sub-issue of Joshi’s entitlement to its provisional’s filing date.

The Federal Circuit disagreed, holding that the issue was never actually litigated in the ’888 litigation.  According to the Court, failing to distinguish between a provisional and non-provisional application during the earlier litigation, without more, did not mean Joshi’s priority date was actually litigated, even though Joshi’s priority date may have been a potentially important question during that litigation.  The Court noted that Purdue neither stipulated that Joshi qualified as prior art nor argued that Joshi did not qualify as prior art.  Thus, the Board conflated the issues of collateral estoppel and res judicata, and incorrectly found that collateral estoppel applied to issues that could have been, but were not, raised in the prior litigation.

Litigants should be aware that silence on an issue (i.e., prior art priority dates) during a previous litigation does not preclude a subsequent challenge in a separate litigation involving the same party and prior art.