Canada’s Intellectual Property Firm

Double Patenting: A comparative guide between U.S. & Canadian practice

Authored byJeffrey Slater and Julien Verneau

Double patenting has become a common challenge to patent validity in Canada since the decision rendered by the Supreme Court of Canada in Whirlpool Corp. v Camco Inc1 in 2000. The Canadian double patenting doctrine is similar to the U.S. double patenting doctrine, but subtle differences between the two can potentially lead to a fatal double patenting issue for a Canadian patent that would otherwise be easily resolved for its U.S. counterpart under U.S. practice. Similarities and differences between the Canadian and U.S. double patenting doctrines are discussed in this article and some strategies are identified for mitigating double patenting risks in Canada.

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The Supreme Court of Canada held in Whirlpool Corp. v Camco Inc that the prohibition against double patenting has two separate "branches": (1) the "same invention" branch, also known as the "coterminousness" branch; and (2) the "obviousness" branch 2. The "same invention" branch will invalidate any claim of a pending application or issued patent that is identical in scope to a claim of an earlier-issued patent. This branch is conceptually similar to "same invention" or “statutory” double patenting in the U.S. The "obviousness" branch will invalidate any claim of a pending application or issued patent that is not patentably distinct (i.e., novel and non-obvious) from any claim of an earlier issued patent. This branch is conceptually similar to the judicially-created doctrine of “obviousness-type” or “nonstatutory” double patenting in the U.S., although there are significant differences between U.S. and Canadian practices in terms of how such an issue may be overcome.

In recent years, the Canadian Federal Court of Appeal (FCA) decision in Mylan Pharmaceuticals ULC v Eli Lilly Canada Inc3 has clarified the test for obviousness-type double-patenting, emphasizing that there are important distinctions between obviousness-type double patenting and “classical” obviousness.  In particular, the FCA decision clarified that in the obviousness-type double patenting analysis only the  claims of the first patent may be applied as “prior art” against those of the second patent and any other prior art is only relevant insofar as it contributes to the common general knowledge of the skilled person.  Moreover, the FCA decision in Mylan Pharmaceuticals ULC v Eli Lilly Canada Inc. emphasized that because the ordinary rules of claim construction apply in the comparison, if the claims of the first patent are unambiguous, it is improper to refer to the specification to vary the scope of the claims of the first patent for the purposes of the double-patenting analysis.

Contrast between Canadian and U.S. double patenting laws

In the U.S., "same invention" double patenting is fatal, whereas “obviousness-type” double patenting can often be obviated with a terminal disclaimer. A terminal disclaimer disclaims the non-overlapping term of the later-issued patent and also provides that the later-issued patent will cease to be enforceable if it does not remain commonly owned with the earlier-issued patent. In contrast, Canadian patent law does not provide any equivalent to a U.S. terminal disclaimer. Due to this difference, greater care must be taken to avoid "obviousness" double patenting situations in Canada that may have been dealt with by way of a terminal disclaimer in the U.S. counterpart.

In Canada, the judicially created double patenting doctrine appears to have been created to prevent patent owners from extending patent protection beyond the statutorily afforded term.  Prior to amendments to the Canadian Patent Act on October 1, 1989, which changed the term for a Canadian patent from seventeen years from patent issuance to twenty years from the filing date, patent applicants could theoretically extend their patent term without end.  For example, an applicant could successively file a series of patent applications covering the same or similar subject matter, with slightly different claims before the first filed patent is issued.  Canadian courts have referred to this problem as the “evergreening” of patent term.

It has been argued that the “sin” of double patenting was removed for applications filed since October 1, 1989 because the term of a patent is now calculated from the filing date regardless of the date of issue of the patent, thereby effectively precluding the possibility of indefinite “evergreening”.  However, Canadian courts have affirmed that a later issuing patent may be invalidated for double patenting on the basis of an earlier issuing patent even in cases where the two patents expire on the same day4.  For example, a double patenting issue may still arise, and the Canadian Intellectual Property Office typically raises this issue, between a parent and a divisional, even though both patents would expire on the same day.

Like the U.S., if a Canadian examiner effectively forces the filing of a divisional application by raising a lack of unity of invention objection (equivalent to U.S. restriction/election requirement), then the claims retained in the parent and the claims divided out are immune from double patenting attacks based on one another. However, Canadian practice differs from U.S. practice on this point in that the limited immunity provided under Canadian practice is purely based on Canadian case-law5, whereas the similar immunity provided under U.S. practice is conferred directly from statute by 35 U.S.C. §121 (the Safe Harbor provision).

Typical double patenting problems 

In general, potential double patenting risks may arise in any situation where the claims of one application arguably fail to recite any further non-obvious element or limitation in comparison to the claims of another co-pending application or issued patent owned by the same entity.

Selection patents

One common scenario in which obviousness-type double patenting can arise relates to selection patents. For example, an initial patent application may be filed with claims to a broad class or genus of compounds. Subsequent work may identify a specific compound or species within the genus that has some advantage over other compounds within the genus, and a selection patent application may be filed with claims for the narrower species. The Supreme Court of Canada has confirmed that selection patents are not, per se invalid for lack of novelty, obviousness or double patenting6. In this decision, the Court found that there was no double patenting in a later issuing selection patent claiming clopidogrel and its hydrogen sulfate salt over an earlier issued patent of the same applicant that claimed the genus encompassing clopidogrel and its salts. However, it is not uncommon for a narrower species application to proceed through examination to issuance more quickly than the earlier filed genus application. In the U.S., if the later-filed species application were to issue first, the still-pending genus application may receive an obviousness-type double patenting rejection which, as noted earlier, could be overcome by filing a terminal disclaimer. As discussed above, no procedural equivalent to a terminal disclaimer exists in Canada.

Continuation practice vs voluntary divisional applications

A further example stems from the fact that Canadian law does not include any direct equivalent of U.S. continuation practice. While Canadian practice does permit the filing of voluntary divisional applications (Canadian Patent Act, Subsection 36(2)), care must be taken to ensure that the claims that issue for a voluntary divisional application are patentably distinct (novel and non-obvious) from the claims of the parent. This can be particularly problematic if a voluntary divisional is filed to pursue the claims of a corresponding U.S. continuation that includes claims that are broader than those of the parent. Due to the absence of any terminal disclaimer or equivalent remedy in Canada, the issuance of the narrower parent claims while the broader divisional claims are still pending could prove fatal to those broader divisional claims.

Multiple applications

Another common scenario arises when multiple applications with substantially identical disclosures but different claim sets are filed on the same day. Even if the independent claims of each application are directed to a different inventive concept than the independent claims of the other applications, the dependent claims often combine the various inventive concepts together, leading to double patenting problems when one of the applications issues.

Strategies for avoiding double patenting problems 

From a foreign practitioner's standpoint, a proactive measure to avoid double patenting problems in Canada is to consolidate all related applications for the same applicant or assignee with a single Canadian patent agent and to inform the Canadian patent agent of the relationship. Even the most diligent Canadian practitioner will be unable to proactively avoid double patenting problems if he or she is unaware that a related application is being prosecuted by another firm.

Developments in the prosecution of U.S. and other foreign counterpart and related applications may also serve as alarm bells to indicate that a review of related Canadian applications would be beneficial. In particular, whenever a terminal disclaimer is filed in the U.S., informing the Canadian agent and instructing him or her to conduct an immediate comparison of the two corresponding Canadian applications may be beneficial, to assess whether the absence of any equivalent terminal disclaimer procedure in Canada may pose obviousness-type double patenting risks.

Claim consolidation is a valuable strategy for avoiding double patenting problems in situations where multiple claim sets are supported by the specification of a single application. This may include situations involving a parent application and its pending or proposed divisional application, or situations involving multiple applications with substantially identical disclosures filed on the same day. Combining two desired claim sets into a single application will result in the examiner either allowing both claim sets to co-exist in the same application, or issuing a unity objection. The unity objection would then permit a divisional application to be filed, and the divisional and its parent would then enjoy a judicial immunity against double patenting attack which they would not have enjoyed if the divisional had been voluntarily filed without any such objection. In either case, double patenting risks are avoided.  Moreover, there are no government fees for excess claims or multiple dependencies in Canada, which means that applicants have considerable leeway in developing optimal claim sets for their Canadian applications.

For other situations, there are procedural mechanisms available under Canadian practice to control the relative timing of the applications. This control can be used to cause a broader "genus" application to issue before a narrower "species" application, thereby ensuring that the later-issued claims are inventive over the earlier-issued claims. The control of the timing of applications can also be used to keep a parent patent application pending as long as possible, until the applicant has determined all of the claims the applicant ultimately wants to pursue. The claims can then be consolidated into the parent application as discussed above, rather than filing a voluntary divisional application.

To control the relative timing of applications, a number of techniques are available to accelerate or decelerate the examination of an application.

Prior to the coming into force of the new Canadian Patent Rules on October 30, 2019, an application could always be abandoned and reinstated as of right within 12 months of the abandonment, no matter the circumstances of the abandonment.  However, when the new Canadian Patent Rules came into force on October 30, 2019 the time window within which reinstatement as of right is available was shortened from 12 months to as little as 6 months in certain circumstances (e.g., failure to timely pay a maintenance fee or to request examination and pay the prescribed fee). A showing of “due care” is now needed once the shortened time window for reinstatement by right has expired in those cases. Because it is unclear what will be deemed to amount to “due care” by the Canadian Intellectual Property Office, in those specific circumstances where a shortened time window for reinstatement by right is applicable Applicants should ensure that the necessary steps to reinstate the application before the “due care” standard becomes applicable.

In the case of an application having a Canadian (or PCT) filing date on or after October 30, 2019, an Applicant could however defer examination in Canada for a period of up to four years after the filing date. In the case the Applicant lets the application go abandoned for failing to request examination within the prescribed deadline, the application can still be reinstated as of right within six months of the prescribed deadline.

Another mechanism to maintain pendency of an application that has received a notice of allowance is to request withdrawal of the notice of allowance under subsection 86(17) of the Patent Rules.  Such a request must be accompanied by a prescribed fee but does not require a stated reason for the request.  In response to such a request the application will be returned to the Examiner for further examination and subsequent notices of allowance can likewise be requested to be withdrawn in order to extend the pendency of the application.

Conversely, there are a number of measures that may be available for expediting examination of a Canadian patent application. These include the use of Patent Prosecution Highway programs and requesting examination of an application out of its routine order upon payment of a government fee or in connection with patent applications relating to “green technology”. It is also possible to expedite examination by requesting examination early and addressing formal matters before substantive examination commences.

Finally, although there is no direct equivalent to a U.S. terminal disclaimer under Canadian practice, Canadian Courts have held that a dedication to the public of certain claims of a patent may be an effective way to overcome a double patenting attack, as long as the dedication does not provide the patentee with an extension of patent term67.


Unwary applicants may face risks associated with one or more of the unique aspects of Canadian double patenting laws. Fortunately, procedural mechanisms, such as those discussed above, are available to mitigate these risks.

For more information, please contact a member of our patents groups.

The preceding is intended as a timely update on Canadian intellectual property and technology law. The content is informational only and does not constitute legal or professional advice. To obtain such advice, please communicate with our offices directly.


  1. Whirlpool Corp. v. Camco Inc., 2000 SCC 67, [Whirlpool].
  2. Whirlpool, supra at paras. 157-159
  3. Mylan Pharmaceuticals ULC v Eli Lilly Canada Inc, 2016 FCA 119 [Mylan]
  4. GlaxoSmithKline Inc. v. Apotex Inc., 2003 FCT 687 at paras. 89 to 91 [GlaxoSmithKline]
  5. Consolboard Inc. v. Macmillan Bloedel Ltd., [1981] 1 SCR 504 [Consolboard]
  6. Merck Co. v. Canada (Minister of Health), 2010 FC 1043 [Merck]
  7. Abbott Laboratories v. Canada (Minister of Health), 2009 FC 648, reversed in part 2010 FCA 168 [Abbott]