A Canadian Federal Court of Appeal  decision earlier this year confirmed the  presence of the “promise of a patent”  doctrine in Canada, meaning that if a  patent application sets out an explicit  promise of an invention’s utility and  the invention is found not to fulfill this  promise, the patent could be found  invalid.

In the case, Sanofi-Aventis v Apotex, the Federal Court of Appeal set aside  a 2011 judgment by the Federal Court,  which had found Sanofi-Aventis’s Plavix  patent invalid. It found the patent to be  valid, consistent with a 2008 Supreme  Court of Canada decision.

The patent at issue was a selection  patent which claimed only one  configuration of a substance having  an identical molecular formula as the  racemic mixture, which comprises two  mirror image configurations, claimed in  the genus patent.  While the selection  – at least in one aspect – fell within the  scope of the genus patent, it provided  special advantages not disclosed in  the genus patent. The Supreme Court  explained that in this case it must be  acceptable to read the specification in  the patent to determine the inventive  concept of the claims.

Reference to the specification enabled  the Federal Court judge to conclude  that inferences over the drug’s utility  amounted to a “promise” which was  found not to be fulfilled, meaning the  patent was invalid. The Federal Court  of Appeal found the patent to be valid  and, at the same time, confirmed the  “promise of a patent” doctrine with the  qualification  that only in cases where  the specification sets out an explicit  "promise" will utility be measured  against that promise.

Where exactly the line of “explicitness”  will be drawn is difficult to predict for  any given patent.  Guidance for the  future may be found in earlier Supreme  Court decisions which have always  accepted that the true interpretation of  a patent can be reached by considering  what a competent workman, reading  the specification at its date, would have  understood it to have disclosed and  claimed.