Watch What You Say! Prosecution History Estoppel in Canada

January 11, 2021

The doctrine of prosecution history estoppel (or file wrapper estoppel) is, of course, well known to practitioners in the United States.  In Canada, however, the use of prosecution history in litigation proceedings was strictly impermissible for many years.  The clearest statement of the law in this regard was the Supreme Court of Canada’s decision in Free World Trust v. Electro Santé (2000 SCC 66), which confirmed that a patent’s prosecution history is “extrinsic evidence” that cannot be considered when the patent is being construed.  That prohibition ended in 2018 when the Patent Act was amended to include section 53.1, which allowed certain submissions made during the prosecution of a patent application to be introduced as evidence for construing granted claims.  Since then, section 53.1 has been regularly invoked when patent claims are asserted and the accused infringer seeks to limit their scope.

In the recent decision of Allergan Inc. v. Sandoz Canada Inc. et al. (2020 FC 1189) the Federal Court identified an interesting limitation to section 53.1.  In particular, Allergan stipulates that the prosecution history may only be introduced into evidence in cases where the patentee is a party to the litigation.  While this decision may help to avoid the prosecution history pitfall in some limited situations, given that the patentee is typically a party to an infringement proceeding, care must nevertheless be taken during the prosecution phase of a patent application to avoid any undue restriction of patent scope later on. 


Section 53.1 of the Act allows for any written communications made by the patentee to the Canadian Intellectual Property Office (“CIPO”) to be admitted into evidence “to rebut any representation made by the patentee in the action or proceeding as to the construction of a claim”.  Section 53.1 stipulates that such communications must have been made during the prosecution of the application for the patent or in a disclaimer or re-examination proceeding in respect of the patent.  Very soon after its introduction, section 53.1 has been relied upon in a number of instances where the claims of a patent were challenged.  The leading decision on section 53.1 is Canmar Foods Ltd. v. TA Foods Ltd. (2019 FC 1233).

In Canmar, the patentee, Canmar, sued TA for infringement of Canadian Patent No. 2,582,376.  The defendant brought a motion for summary judgment of non-infringement and argued that section 53.1 applied for the purposes of claim construction.  The ‘376 patent is directed to a method for roasting oil seeds and the sole independent claim (claim 1) recites four steps.  During the course of prosecution of the ‘376 application, the CIPO issued one substantive objection in which the originally filed claims were alleged to lack inventiveness.  In response, Canmar amended claim 1 to incorporate two further elements: (i) heating the oil seed in a “stream of air”; and (ii) transferring the heated seeds “into an insulated or partially insulated roasting chamber or tower”.  Canmar also stated in its response to the CIPO that the claims as amended “correspond substantially” with the claims of the related U.S. application and simply that the amended claims were novel and non-obvious.

In its analysis, the court confirmed that:

With the introduction of section 53.1, purposive construction of patent claims in Canada now includes three prongs: (1) the claims themselves; (2) the disclosure; and (3) the prosecution history in Canada, when used to rebut a representation made by the patentee as to the construction of a claim in the patent” (Canmar, [68]). 

The court then concluded that the added elements (i) and (ii) were essential to claim 1 both on a plain reading of the claim and having regard to the prosecution history.  The court also found that the method used by TA did not include these two features and, therefore, did not infringe claim 1 (or, by extension, any of the remaining dependent claims).  The court granted TA’s motion for summary judgment.

It is important to note that in Canmar the defendant argued that the prosecution history of Canmar’s related U.S. application must also be considered under section 53.1 in addition to the Canadian prosecution history.  This argument was predicated on the fact that in its response to the CIPO, the patentee did not directly address the objections raised but only indicated that the claims were being amended to substantially correspond with those of the U.S. case and were novel and non-obvious.  The court agreed with TA and noted:

Extraordinary circumstances arise where, as in this case, the patentee acknowledges that the claims have been amended to be substantially the same as claims submitted in another jurisdiction, and the patentee admits that the amendments have limited the scope of the claims in order to make the claims novel and non-obvious. In these circumstances, the Court should be able to refer to the foreign prosecution history for the limited purpose of purposively construing the Canadian claims.” (Canmar, [74]; emphasis in original).

In the extraordinary circumstance that prosecution of the foreign application is made part of the prosecution history of the Canadian patent, that foreign prosecution history, where relevant to limitations made to Canadian claims, should be admissible to aid in a purposive construction of the claims of the Canadian patent.” (Canmar, [77]; emphasis in original). 

The court went further to suggest that similar “extraordinary circumstances” arise in applications that are prosecuted under the Patent Prosecution Highway (PPH) program, where, by necessity, the claims in Canada are voluntarily amended to conform to claims allowed in a foreign jurisdiction. 

Canmar has appealed the Federal Court’s decision and that outcome is awaited. 

The Allergan Decision

Canadian Patent No. 2,507,002 is directed to the drug silodosin and was issued to Kissei Pharmaceutical Co. Ltd.  Allergan is the exclusive licensee of the ‘002 patent and is authorized to market silodosin in Canada.  Sandoz sought to obtain a Notice of Compliance (NOC) for marketing silodosin.  In turn, Allergan commenced an action in Federal Court under the Patented Medicines (Notice of Compliance) Regulations to prevent Sandoz from obtaining its NOC, alleging that Sandoz’s product would infringe the ‘002 patent.  Sandoz denied the infringement allegation and counterclaimed that the ‘002 patent was invalid for obviousness.  It is important to note that the patentee, Kissei, while not taking any position on the issue of infringement, denied the invalidity allegations and did not appear at trial or make any submissions.  Sandoz was ultimately successful in its non-infringement allegation but not on its counterclaim of invalidity.

In the course of its analysis, the court undertook the step of construing the relevant claims of the ‘002 patent.  For this phase, Sandoz argued that section 53.1 of the Act should apply and, as a consequence, certain of the claim elements should be considered essential.  The court disagreed. 

Section 53.1 reads as follows:

53.1 (1) In any action or proceeding respecting a patent, a written communication, or any part of such a communication, may be admitted into evidence to rebut any representation made by the patentee in the action or proceeding as to the construction of a claim in the patent if

(a) it is prepared in respect of

(i) the prosecution of the application for the patent,

(ii) a disclaimer made in respect of the patent, or

(iii) a request for re-examination, or a re-examination proceeding, in respect of the patent; and

(b) it is between

(i) the applicant for the patent or the patentee; and

(ii) the Commissioner, an officer or employee of the Patent Office or a member of a re-examination board.

While acknowledging that section 53.1 provides an exception to the prohibition of relying on extrinsic evidence during a claim construction exercise, the court held that this exception can only be put in play to rebut representations made “by the patentee”.  Given that the action in this instance was brought by the licensee (Allergan) and that the patentee made no representations with regard to claim construction, the court concluded as follows:

In summary, the plain and ordinary meaning of the language in subsection 53.1(1), together with a contextual reading of the Act and the jurisprudence discussed above, support the view that the word “patentee” in subsection 53.1(1) does not include a licensee… Accordingly, given that no representation has been made by the patentee (Kissei) of the ‘002 Patent in the present action, the file prosecution history is not admissible in evidence in this action.”  (Allergan, [133].)

In arriving at this conclusion, the court noted that Parliament was aware of this “loophole” in section 53.1, but nevertheless chose to adopt the final language (Allergan, [131]-[132]).  Perhaps to foreshadow future issues, the court also stated in obiter:

I will simply observe in passing 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).” (Allergan, [135]).


Notwithstanding the “loophole” identified by the court in Allergan, it is clear that prosecution history estoppel is and will be continually raising its head in Canadian patent litigation.  As a consequence, prosecution of patent applications before the CIPO should be carefully handled to avoid potential issues later on.  Here are some suggestions:

1. When responding to objections raised by the CIPO, care should be taken to avoid unnecessarily admitting limitations of claim scope or essentiality of claim elements. 

2. Section 53.1 makes it clear that only “a written communication, or any part of such a communication” can be relied upon for invoking prosecution history estoppel.  Applicants should therefore consider conducting examiner interviews where possible. 

3. Canadian jurisprudence makes it clear that, in certain circumstances, foreign prosecution history may also be taken into consideration when construing the scope of granted claims.  Thus, when relying on the allowance of a related foreign application for amending claims in Canada, applicants should ensure that the file history of the foreign case is carefully reviewed to ensure that it does not contain any unnecessary or inaccurate statements that may be construed to be limitations or restrictions of claim scope.  



Newsroom Articles

Choose Your Own Source: Adding A Trademark to Someone Else’s Goods

Antonio Turco

In a recent decision arising from an appeal of a decision of the Trademarks Opposition Board, the Federal Court commented on when a retailer can establish use of a trademark on goods when the retailer is not the “source” of the goods. Specifically, if a retailer simply affixes its own trademark to goods manufactured by a third party, does that constitute use of the retailer’s trademark in association with those goods.

Read more

Hot Dog!: Injunction Overturned in “Bombay Frankie” Case

Sarah O'Grady

Interlocutory injunctions in Canadian trademark cases are rare. The decision at first instance to grant a motion for an interlocutory injunction in a dispute related to the “Bombay Frankie” trademark therefore made headlines, at least in trademark circles, for two reasons. First, the fact that the injunction had been granted was in itself noteworthy. Second, many in the intellectual property bar were of the view that the decision misapplied certain fundamental principles of trademark law and therefore introduced uncertainty into the law.

Read more

I Can’t Wait! Speeding Up Processing of Your Canadian Trademark Applications

Anthony Prenol

Canada continues to make news (the wrong kind) when it comes to the slow pace of its examination of trademark applications. Despite repeated promises by the Canadian Intellectual Property Office (“CIPO”) to speed things up, the problem is only getting worse. However, there are some promising signs.

Read more

130 Queens Quay East, East Tower, Suite 809, Toronto, Ontario, M5A 0P6, Canada
Main: (647) 478-2425 | Fax: (647) 478-2438 |
© CPST Intellectual Property Inc.
All Rights Reserved. 2021 |
Legal | Terms of Use
Website Design by Clutch Marketing