An accused device infringes under the doctrine of equivalents when, among others, the alleged equivalent represents an “insubstantial” change from the claim language. Uncertainty arises, however, when the equivalent is itself patented. Would a finding of equivalence amount to a declaration that the patent covering the accused device is invalid? Perhaps to avoid this outcome, the Federal Circuit has held that a finding of equivalency in this scenario is “considerably more difficult to make out,” albeit not necessarily foreclosed.
In a recent opinion, district judge Sue L. Robinson faced, and declined to wade into, this separate patentability issue in the preliminary-injunction context. Acknowledging that the equivalent’s patented status is evidence that it was “previously unknown and/or non-obvious,” and that customers in the field accepted the interchangeability of the compounds in issue, the Court nonetheless rejected the notion that plaintiff could show a likelihood of success on the merits.
According to the Court, defendant has a “strong argument” that, as a matter of law, the equivalent is both novel and substantially different from the asserted invention. “To the extent that ‘known interchangeability’ can coexist with separate patentability, plaintiff’s burden on its preliminary injunction motion is a heightened one.”
Perhaps the result would be different had this been an actual finding on the merits?