Canadian law relating to double patenting is very strict compared with other countries. To obtain a second patent for the closely related subject matter, the claims must be patentably distinct.  In contrast, in most other countries, a difference in claim scope will generally support the grant of a second patent.  This distinction often catches patent applicants, particularly from other countries, off guard.  A recent decision of the Canadian Patent Appeal Board in respect of Canadian patent application No. 2444597 covering FAB I inhibitors (Commissioner’s Decision No. 1430) reflects Canada’s strict position.

The ‘597 application includes claims directed to a single compound. The Examiner alleged this compound was not patentably distinct from a group of compounds claimed in an earlier patent No. 2387016 owned by the same entity, and therefore rejected the ‘597 application on the basis of double patenting.  The Patent Appeal Board upheld that decision.

In this case, the applicant argued that the compound claimed in the ‘597 application, which fell within the genus of compounds claimed in the ‘016 patent, had improved antimicrobial properties as compared with the previously claimed compounds and therefore was a patentably distinct selection from the earlier genus. However, the Board determined that the claimed compounds of the ‘016 patent purported to be just as effective as those claimed in the ‘597 application, and that there was no special advantage of the claimed compound of the ‘597 application over the earlier compounds disclosed in the ‘597 specification.  The Board further determined, without acceding that such evidence was relevant given that disclosure of the special advantage required to support a selection patent must be in the specification, that post-filing data comparing the efficacy of the compound of the ‘597 application against only one of the compounds disclosed in the ‘016 patent with was not persuasive to establish increased efficacy.  The Board considered that the experimental post-filing data did not represent a fair comparison of efficacy since some variability in efficacy among the claimed genus of compounds was to be expected and one compound could not be taken to be representative of the genus.

This decision reiterates the importance of presenting all desired claims early in Canadian prosecution, to avoid the need to later file divisional applications having claims of differing scope that may be rejected on the basis of double patenting.