In this case, the Federal Circuit held that, depending on context such as prosecution history, amending patent claims to use the transitional phrase “consisting essentially of” may limit the claims to exclude other elements that do not materially affect the basic and novel properties of the invention as claimed. The case involved U.S. Patent No. 8,293,742, which claimed methods for reducing eye redness using brimonidine. During prosecution, the claims were amended by replacing the broader term “comprising” with the narrower phrase “consisting essentially of” to overcome prior art that required the use of an additional active ingredient, brinzolamide. The claims were subsequently allowed based on the argument that the amended claims did not include any other active ingredients.
In an inter partes review (IPR) proceeding, the Patent Trial and Appeal Board (PTAB) applied the conventional interpretation of “consisting essentially of”, allowing the inclusion of unlisted ingredients that do not materially affect the basic and novel properties of the invention. However, the Federal Circuit reversed, finding that the prosecution history showed a clear intent to limit the invention to only brimonidine as the active ingredient. The Federal Circuit concluded that, in this context, “consisting essentially of” excluded other active agents based on the explicit statements provided during the prosecution history, particularly the argument that amending the claims from “comprising” to “consisting essentially of” meant the claims did not include any other active ingredients.
Written by Mason Muskett, 2025 Summer Associate