The Supreme Court of Canada has issued a decision finding that Pfizer’s Canadian patent No. 2,163,446 for Viagara is invalid, following an appeal by generic drug manufacturer Teva Canada Limited challenging the patent’s validity in a notice of compliance proceeding. This decision paves the way for Teva to obtain regulatory approval to sell a generic version of sildenafil (the generic name for Viagara) in Canada prior to the 13 May 2014 expiration date of the ’446 patent.

The Supreme Court of Canada found the ’446 patent to be invalid for insufficient disclosure. Specifically, Pfizer stated in the application that “one of the especially preferred compounds” worked to treat erectile dysfunction (based on a study that had been conducted). However, the application did not disclose the identity of the compound that worked. The claims of the ’446 patent covered many compounds, and specifically claimed two compounds. One of these compounds was sildenafil, but the other was a compound that is not useful to treat erectile dysfunction. Because a skilled person would need to conduct further testing to determine which of the two specifically claimed compounds would work to treat erectile dysfunction, the Court concluded that the disclosure requirements of the Patent Act had not been met.

In deciding that the ’446 patent is invalid, the Court emphasized that the grant of a patent is a bargain: society grants the patent holder a time-limited monopoly in exchange for being provided with proper disclosure of the invention and how it works.

The full text of the decision of the Supreme Court of Canada is available here.