In a cautionary tale to be heeded by patent drafters, the Supreme Court of Canada held that Pfizer's patent directed to sildenafil, better known as Viagra, is invalid for failing to meet the disclosure requirement of section 27(3) of the Patent Act. An attack on the validity of the patent by the generic company, Teva, in the context of a section 55.2 proceeding under the Patented Medicines (Notice of Compliance) Regulations was unsuccessful before both the Federal Court and the Federal Court of Appeal.

The decision of the Federal Court garnered attention by reason of the Court expressing in obiter, its discomfort with the fact the patent played "hide and seek with the reader." The Court questioned why the disclosure did not simply identify the only compound tested as sildenafil (as claimed in claim 7).

In the patent at issue, claim 1 encompassed 260 quintillion compounds while the dependent claims were progressively narrower. Claims 6 and 7 were each directed to one compound. In the disclosure, it was noted that "one of the special preferred compounds" had been shown to be effective in treating erectile dysfunction (ED). The evidence before the Court was that only sildenafil, the subject of claim 7, was the effective compound. The disclosure, however, did not specifically identify sildenafil as the compound that was effective in treating ED. The Supreme Court of Canada recognized that a person of ordinary skill in the art could look to the claims and note that two claims were directed to the use of individual compounds, which might suggest to the skilled person that the invention was directed to those compounds. However, the Court also found it would have taken a "minor research project" to identify the true invention. On this basis, the Court found the disclosure failed to meet the requirement of section 27(3) of the Patent Act in that the specification did not correctly and fully describe the invention and its use as contemplated by the inventors because the patent would not have enabled the skilled person to produce the invention using only the instructions contained in the description.

The Court also considered the issue of utility. While in the last few years, the Courts had appeared to raise the bar on the issue of utility, this decision appears to swing the pendulum back by holding that since, at the time of the filing of the application, sildenafil could assist in treating ED, this was sufficient to meet the utility criterion.

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