Yesterday, Mon., Apr. 9, 2012, in Aventis v. Hospira, No. 2011-1018, the Federal Circuit (Linn, Dyk, and Prost) applied the Therasense inequitable conduct standard to affirm a district court’s ruling that two patent were unenforceable based on withheld prior art.  This may be the first Federal Circuit decision to affirm inequitable conduct under the stricter Therasense standard.

The Court ruled that the two-prong Therasense standard requires (1) showing “but-for” materiality by a preponderance of evidence and (2) showing intent to deceive by clear and convincing evidence.  The Federal Circuit reviewed the district court’s factual findings for clear error and the ultimate unenforceability ruling for abuse of discretion.