Perhaps more than any other technology field, patentees in the life sciences sector tend to be holders of patent families: collections of patents and applications relating to a single general research program, or reflective of incremental advances. This strategy is often desirable, and may be necessary to ensure effective patent protection for all new inventions stemming from the research. At the same time, vigilance is required to ensure the filing and prosecution strategy does not render key patent claims vulnerable to later double-patenting attacks.

Under the Canadian Patent Act, a patentee is entitled to only “a patent for an invention.” This seemingly straightforward principle is the only statutory basis for the prohibition on double-patenting. However, double-patenting attacks on patent validity and objections by examiners in prosecution are becoming increasingly common. In response to this heightened level of scrutiny, the law regarding double-patenting has become increasingly complex, and to some extent uncertain.

As a first general point, only later-filed, and co-owned, patents or applications may be cited against earlier-filed documents. Nevertheless, there is no terminal disclaimer practice in Canada, and even divisional applications stemming from the same parent, and therefore expiring on the same date, are potentially citable against one another. Recent Patent Office practice increasingly cites applications in both directions, even asserting that earlier-filed claims “cannot be issued in a separate patent” from later-filed claims. Although such an objection may appear illogical, in cases where a later-filed application has already issued and an earlier filed application is still pending, there may be a valid basis for bringing such a double-patenting issue to the applicant’s attention.

With respect to co-pending divisional applications, the Supreme Court has held that “enforced divisionals,” meaning divisional applications filed in response to a lack of unity objection by the Patent Office, should not be vulnerable to a later double-patenting attack in view of the parent application. However, the Federal Court recently held that where subsequent amendments to the claims of the divisional application result in overlapping or “obvious” subject matter, when compared with the claims of the parent, such a divisional is no longer protected by the enforced divisional shield, and may be invalid.

As a second general point, there are two branches to the Canadian prohibition on double patenting: same invention double-patenting and obviousness double patenting. The assessment under the first branch, same invention double-patenting, is relatively straightforward: if the claimed subject matter overlaps with any claim of a citable patent or application, the subject claim is invalid. An exception to this branch, however, does apply in the case of valid selection patents.

When making an assessment as to obviousness double-patenting, courts have held the two sets of claims must be considered from the perspective of one skilled in the art, but not in light of any cited prior art. This makes achieving consistent and predictable results in prosecution more difficult, as examiners will tend to rely on certain assumptions as to the state of mind of the skilled person as of the relevant date. Furthermore, there is no doctrine of file wrapper estoppel in Canada, and the findings of a Court with respect to a question of double-patenting may be completely inconsistent with the findings of an examiner in respect of the same question.

As a third general point, it should be noted that the prohibition against double patenting involves a comparison of the claims only. Courts have clearly held that the disclosure, as well as the prior art, should not be considered when making a double-patenting assessment. By contrast, any portion, including the disclosure or the claims, of an earlier-filed third-party owned Canadian application may be cited against a later-filed application for anticipation.

Regardless of whether a patentee, or even an examiner, considers a later-filed patent or application to constitute double-patenting in view of an earlier-filed patent or application, a court may find otherwise in a later invalidity action. Thus, care must be taken to minimize the vulnerability of any later-filed patent claims to such an attack.

In short, when assessing a patent family for possible double-patenting issues, patentees must consider all co-owned patents and applications that relate in any way to one another, regardless of filing date or common parent application.

Canadian double patenting law is continually changing and adapting as courts are forced to address new forms of double-patenting attacks. Life sciences patentees, particularly the holders of patent families, should take great care to ensure each of their applications is carefully reviewed in view of all co-owned patents and applications prior to grant, to ensure that no unexpected double-patenting issues will arise in later litigation.