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OxyContin® Patents Are Unenforceable for Inequitable Conduct

June 07, 2005

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Last Month at the Federal Circuit - July 2005

Judges: Plager (author), Gajarsa, and Linn

In Purdue Pharma L.P. v. Endo Pharmaceuticals, Inc., No. 04-1189 (Fed. Cir. June 7, 2005), the Federal Circuit affirmed a district court’s decision that certain patents found to be infringed by generic versions of OxyContin® were unenforceable because of inequitable conduct that occurred during prosecution of the applications leading to these patents.

The three patents at issue, U.S. Patent Nos. 5,656,295 (“the ‘295 patent”), 5,508,042 (“the ‘042 patent”), and 5,549,912 (“the ‘912 patent”) are directed to controlled-release oxycodone medications for treatment of moderate to severe pain. The ‘912 patent is a CIP of U.S. Patent No. 5,266,331 (“the ‘331 patent”), which was not asserted. Purdue Pharma L.P. and other related companies (collectively “Purdue”) asserted the three patents-in-suit against Endo Pharmaceuticals, Inc. and a related company (collectively “Endo”).

The detailed description of each of the patents includes the following statement, which played a prominent role in the determination of inequitable conduct. “It has now been surprisingly discovered that the presently claimed controlled release oxycodone formulations acceptably controlled pain over a substantially narrower, approximately four-fold [range] (10 to 40 mg every 12 hours—around the clock dosing) in approximately 90% of patients.” This statement was contrasted with the approximately eight-fold range required for approximately 90% of patients for opioid analgesics in general.

In September 2000, Endo filed an ANDA with the FDA seeking approval to make and sell a generic version of Purdue’s OxyContin® formulation. Purdue had by that time listed the three patents-in-suit in the Orange Book as covering OxyContin®. In October 2000, Purdue initiated a patent-infringement suit on the basis of Endo’s ANDA filing. The trial court found that Purdue had shown that Endo’s proposed generic drug products would infringe Purdue’s patents. The trial court further concluded, however, that Endo had also shown that Purdue’s patents were invalid due to Purdue’s inequitable conduct during prosecution of the patents before the PTO. The district court had found that the foregoing statement from the specification concerning Purdue’s alleged discovery for controlling pain over a four-fold range of doses compared to an eight-fold range for opioids failed to inform the PTO that such discovery was based on insight without scientific proof.

The Federal Circuit agreed that Purdue’s comments in its specification were material for purposes of 37 C.F.R. § 156(b). Purdue simply had no clinical evidence supporting its claim at the time it was made or at any time before the patents issued. Purdue contended, however, that any lack of scientific proof of the four-fold dosage range for oxycodone was irrelevant because the inventors never stated during prosecution of the patents that the discovery had been clinically tested. The Court agreed that Purdue made consistent representations of the four-fold dosage range for controlled-release oxycodone as a “surprising discovery” in order to distinguish prior art. Accordingly, it could not say that the trial court had clearly erred in finding that Purdue had failed to discover material information. While Purdue had never expressly stated that the discovery of the four-fold dosage range was based on the results of clinical studies, that conclusion was clearly to be inferred from the language used by Purdue in both the patents and the prosecution history.

The Federal Circuit agreed with the district court concerning the materiality of Purdue’s statement, recognizing that Purdue’s statement was consistently used throughout the prosecution history of the patents-insuit to distinguish prior art and was made to suggest or infer that the results touted were based on clinical studies. The Court noted that under the PTO’s current materiality standard, information may be material if it refutes or is inconsistent with the applicant’s patentability arguments, which may be independent of the claims. As to intent, in this case, intent to mislead the PTO can be inferred from Purdue’s statements in the context in which they were made. Purdue’s carefully chosen language suggested that it had obtained clinical results, and that suggestion was left unclarified by any disclosure that discovery of the four-fold dosage range of oxycodone was based on insight. The Court observed a clear pattern of misdirection throughout the prosecution of the patents.