File Wrapper Estoppel In Canada

The Canadian Patent Act was amended last year to include a new provision which allows prosecution histories into evidence in patent proceedings to rebut representations made by the patentee regarding claims construction.

This amendment overturned the longstanding principle in Canadian patent law that claims are to be construed without regard to extrinsic evidence, including statements made during prosecution. This amendment may result in the adoption of file wrapper estoppel or a similar rule of claims construction in Canada; however, its application remains subject to judicial interpretation.

The History of File Wrapper Evidence in Canada

In the U.S., patent prosecution histories (also known as "file wrappers") are regularly considered in the claims construction analysis, where the principle known as prosecution history estoppel (or file wrapper estoppel) precludes patentees from asserting a position regarding claims construction during litigation that is inconsistent with the patentee's statements made to the USPTO during prosecution. For example, where an applicant makes representations during prosecution that limit the scope of a claim in order to avoid prior art, that patentee cannot later argue for a wider scope of the claim when asserting the patent in infringement proceedings.

In contrast, in Canada, there was a longstanding principle which provided that claims are to be construed without regard to extrinsic evidence (see Free World Trust c. Electro Santé Inc, 2000 SCC 66). In Free World Trust, the Supreme Court of Canada expressly rejected the principle of file wrapper estoppel and stated:

To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation. The current emphasis on purposive construction, which keeps the focus on the language of the claims, seems also to be inconsistent with opening the pandora's box of file wrapper estoppel. Notwithstanding the Supreme Court of Canada's comments in Free World Trust, in subsequent cases the Federal Court has relied on amendments made to claims during prosecution. For example, the Court has held that such amendments are "objective facts" that may be considered in construing the claims (Distrimedic Inc v Dispill Inc, 2013 FC 1043, at para 210; Eli Lilly Canada Inc v Mylan Pharmaceuticals ULC, 2015 FC 125 at para 154)


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