Continuing to refine Canada’s “file wrapper estoppel”

File wrapper estoppel, a well-known doctrine under U.S. patent law, is based on the general principle that an applicant cannot make representations to the patent office to avoid refusal of a patent application, and then during litigation of the patent, assert that the patent covers features of the invention conceded during prosecution. Historically, representations made to the Canadian Intellectual Property Office (CIPO) during a patent’s prosecution have been inadmissible for the purpose of construing the claims in litigation. However, in December 2018, the Patent Act (the Act)1 was amended to allow courts to consider written communications to the CIPO during prosecution to rebut a representation made by a patentee about the construction of a claim. In the latest update from our IP team, we provide updates on the continuing refinement of Canada’s version of “file wrapper estoppel”.

What you need to know

  • No bright line yet between admissible and inadmissible statements made during prosecution. It remains unclear when statements made during the prosecution of a patent are admissible as evidence during litigation. Therefore, it is very important that caution be exercised when communicating with the CIPO during prosecution.
  • Comments in foreign patents may be admissible. General statements made to the CIPO about related, foreign patents during prosecution of a Canadian patent should typically not be readily admissible during litigation. However, until there is further clarity, patent applicants should be mindful of their written comments to the CIPO regarding foreign applications and patents.
  • Only statements made by patentees are admissible. In contrast to representations made by the patentee during litigation of a patent, representations made by a licensee or any other person claiming under the patentee in an action or proceeding in respect of the patent, cannot be used as a basis to admit into evidence statements made by the patentee during prosecution.
  • Co-ordination between patentee and licensee during prosecution is key. All interested parties should carefully consider what written communications should be made to the CIPO during prosecution and during post-grant procedures, such as disclaimers, re-examinations and reissues in order to optimally plan for litigation, should it arise.

The Canadian version of “file wrapper estoppel”

As previously discussed in our bulletins in 2020 and 2019, Canadian courts have historically held that statements made in the prosecution history of a patent are inadmissible in subsequent patent litigation. Prior to the December 2018 amendments to the Act, courts had expressed some concern that one could never look at the file prosecution history to interpret a claim2,3. Section 53.1 of the Act, introduced in 2018, provides a statutory exception to this common law prohibition. It permits “written communications” between the patentee and the CIPO during prosecution of the patent to be relied on in litigation to rebut representations made by the patentee during the action or proceeding about construction of a claim in the patent. Courts have begun to establish the boundaries of this exception, as shown in Bauer Hockey Ltd. v Sport Maska Inc4. when the Federal Court held that as long as the issue is one of claims construction, section 53.1 applies and the prosecution history is admissible. The decisions in CanMar Foods Ltd. v. TA Foods Ltd. (CanMar)5 and Allergan Inc. v. Sandoz Canada Inc. et al. (Allergan)6, discussed below, continue to refine the limits of “file wrapper estoppel” in Canada.

CanMar: Caution when referencing foreign file wrappers

In CanMar, CanMar Foods Ltd. appealed a decision of the Federal Court granting a motion for summary judgement to TA Foods and dismissing CanMar’s patent infringement action against it. In concluding that TA Foods had not infringed CanMar’s patent, the Federal Court relied in part on statements made by CanMar in the prosecution history of the corresponding U.S. patent to determine that certain elements of the claims were essential for infringement. Although section 53.1 of the Act does not address foreign prosecution histories, the motions judge held that the U.S. prosecution history was admissible because it had been specifically referred to in the Canadian prosecution; CanMar appealed. One of the issues considered in the appeal was whether statements made during prosecution of the corresponding US patent were admissible as evidence under section 53.1 of the Act. Although it dismissed the appeal, the Federal Court of Appeal found that the Federal Court judge’s recourse to the U.S. file prosecution history was inappropriate based on the specific circumstances of the matter.

In its decision, the Federal Court of Appeal cautioned against readily admitting foreign prosecution history into evidence. It noted that the language of section 53.1 of the Act is specific to communications with the CIPO, and that it would go against the principles of statutory interpretation to try to go beyond its original intent. Specifically, the Court warned that “[opening] the door to allowing foreign patent prosecution history into the analysis might lead to overly contentious and expensive litigation”, and that because of differences between the patent processes, including differences in the language of the patent claims admitting foreign prosecution evidence can lead to potential issues of translation and interpretation of the claims7. However, the Court stopped short of an absolute bar on the admission of foreign file prosecution histories, recognizing that there may be situations in which a patentee’s statements during prosecution may create a sufficient nexus between the foreign prosecution and the Canadian patent under section 53.1 of the Act.

The Court found that nothing in CanMar’s patent’s prosecution file specifically identified what “written communication” from the U.S. prosecution history was incorporated by the patentee into the Canadian patent file history and where that written communication could be found. The only reference to a foreign “written communication” in the file history was the patentee’s note in an office action response that some of the claims were being amended to “correspond substantially” to those of “a related US application”8. Based on the facts of the case, the Court held that the Federal Court judge should not have considered the U.S. prosecution history.

Allergan: Whose representations can trigger Canada’s “file wrapper estoppel”?

In Allergan, Sandoz Canada Inc. sought approval to market a generic alternative to the drug RAPAFLO® used in the treatment of benign prostatic hyperplasia. Sandoz alleged that its product would not infringe Canadian Patent No. 2,507,002. The patent is owned by Kissei Pharmaceutical Co., Ltd., but licensed to Allergan Inc. who is authorized to market RAPAFLO® in accordance with a series of Notices of Compliance (NOCs) issued by Health Canada. Since Sandoz’s regulatory submissions relied on Allergan’s NOCs, Sandoz served Allergan with a Notice of Allegation under the Patent Medicines (Notice of Compliance) Regulations9. In response, Allergan brought an action in the Federal Court seeking a declaration that the making, construction, using or selling of Sandoz’s generic would infringe the Kissei Patent. Notably, Kissei Pharmaceutical Co., Ltd. (Kissei) did not participate during the trial and merely denied that any of the Kissei Patent claims are invalid and relied on Allergan’s submissions in this regard in the proceeding.

At trial, Sandoz sought to rely on the prosecution history to support its position on claims construction. However, based on the explicit reference to representations made by the patentee in section 53.1 of the Act, and Parliament’s decision not to explicitly include representations made by anyone claiming under the patentee (such as a licensee), the Court found that representations made by Kissei to the Patent Office could not be relied on to rebut representations made by Allergan, as a licensee, during the litigation. Since the section 53.1 exception was not applicable, the general rule applied and the file prosecution history was not admissible into evidence. That said, the Federal Court did comment that “the file prosecution history in question provides a glaring example of the mischief that is implicitly permitted by the current wording of subsection 53.1(1)”10.


1 R.S.C., 1985, c. P-4

2 Distrimedic Inc. v. Dispill Inc., 2013 FC 1043

3 Pollard Banknote Limited v. BABN Technologies Corp., 2016 FC 883

4 2020 FC 624

5 2021 FCA 7

6 2020 FC 1189

7 CanMar at para. 71

8 CanMar at para. 75

9 SOR/93-133

10 Allergan, para. 135.

To discuss these issues, please contact the author(s).

This publication is a general discussion of certain legal and related developments and should not be relied upon as legal advice. If you require legal advice, we would be pleased to discuss the issues in this publication with you, in the context of your particular circumstances.

For permission to republish this or any other publication, contact Janelle Weed.

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