Inequitable Conduct as a Defense to Patent Infringement in the Wake of Therasense: Defining “Materiality” and “Specific Intent”

On May 25, 2011, the U.S. Court of Appeals for the Federal Circuit issued a landmark decision changing the standards for proving inequitable conduct as a defense to patent infringement. In Therasense, Inc. v. Becton, Dickinson & Co., the court held that to establish inequitable conduct an accused infringer must prove, first, that the patentee acted with specific intent to deceive or made a deliberate decision to withhold information from the United States Patent and Trademark Office (“PTO”); and, second, that “but for” the patentee’s misrepresentations or omissions, the PTO would not have issued the patent.

Therasense addressed a patent for disposable blood glucose test strips developed for the treatment of diabetes. The patentee sought to claim glucose strips that lacked a membrane on the electrode used for testing, over prior art stating that a membrane was “optionally, but preferably” included on the test strip. Because the patentee also owned the prior art, the Examiner required a declaration that the prior art had required a membrane. The patentee’s R&D director averred that a person of ordinary skill would understand the prior art’s use of “optionally, but preferably” language as requiring a membrane, and the Examiner allowed the claims. During the earlier prosecution of the European counterpart to the same prior art, the patentee had, however, submitted a declaration, from the same expert, stating that the prior art did not require a membrane. When the patentee asserted the patent against Becton, Dickinson & Co., the alleged infringer argued that it was unenforceable due to the patentee’s inequitable conduct by failing to disclose properly the prior art to the PTO.