Canada's Supreme Court Invalidates Pfizer’s Patent for Viagra


Unlike U.S. patent law, Canadian intellectual property law calls for full disclosure of a drug’s active ingredient in order for a patent to be valid. Last week the Supreme Court of Canada stated “sufficiency of disclosure lies at the very heart of the patent system” and invalidated Pfizer’s patent on the popular erectile-dysfunction drug Viagra for failing to openly disclose the drug’s active ingredient.

In a suit brought by Israeli firm Teva Pharmaceuticals, the court said Pfizer failed to adequately disclose that sildenafil was the active compound, while other listed compounds in the patent were not effective in treating erectile dysfunction:

P holds Patent 2,163,446 for the use of a “compound of formula (I)” or a“salt thereof” as a medicament for the treatment of erectile dysfunction (“ED”). The patent’s specification ends with seven cascading claims for successively smaller ranges of compounds, with Claims 6 and 7 relating to a single compound each. Only sildenafil, the subject of Claim 7 and the active compound in Viagra, had been shown to be effective in treating ED at the time of the patent application. Although the patent includes the statement that “one of the especially preferred compounds induces penile erection in impotent males”, the patent application does not disclose that the compound that works is sildenafil, that it is found in Claim 7, or that the remaining compounds had not been found to be effective in treating ED.

The decision effectively opens up competition in Canada for Viagra substitutes well ahead of what would have been the 2014 patent expiration date.


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