Kaken Pharmaceutical Co., Ltd. v. Iancu, [2018-2232] (March 13, 2020), the Federal Circuit   reversed the PTAB’s claim construction, and vacated its determination that the challenged claims of U.S. Patent No. 7,214,506 on a method for treating onychomycosis were unpatentable as obvious.

Kaken proposed that the phrase “treating a subject having onychomycosis” means “treating the infection at least where it primarily resides in the keratinized nail plate and underlying nail bed.” The Board rejected Kaken’s construction as too narrow, concluding that “the express definition of onychomycosis includes superficial mycosis, which in turn is expressly defined as a disease that lies in the skin or visible mucosa.

The Federal Circuit found that the prosecution history—which includes, specifically, statements made by Kaken to overcome a rejection and the examiner’s statements explaining withdrawal of the rejection based on those statements — provides decisive support for limiting the claim phrase at issue to a plate-penetrating treatment of an infection inside or under the nail plate.  A patent’s prosecution history can “inform the meaning of the claim language by demonstrating how the inventor understood the invention and whether the inventor limited the invention in the course of prosecution, making the claim scope narrower than it would otherwise be.  Particularly useful are “express representations made by or on behalf of the applicant to the examiner to induce a patent grant,” which include “arguments made to convince the examiner that the claimed invention meets the statutory requirements of novelty, utility, and nonobviousness.”  The Federal Circuit said that Kaken’s statements during prosecution, followed by the examiner’s statements, make clear the limits on a reasonable understanding of what Kaken was claiming.

The Federal Circuit thus reversed the Board’s claim construction, and vacated the determination of obviousness based upon the erroneous construction.