Pfizer and Teva have been fighting a legal battle over Pfizer’s patent for Viagra in Canada. The first shot was fired when Novopharm Limited, now Teva Pharmaceutical Industries, applied for a notice of compliance in order to produce a generic version of Viagra in Canada. Teva alleged that Pfizer’s Canadian Patent 2,163,446 was invalid for obviousness, lack of utility and insufficient disclosure. The lower Federal Court held that the patent was valid because the invention was not obvious. The lower court also concluded that the invention was useful, and that the patent did not fail to adequately disclose it. The lower court prohibited the issuance of the notice of compliance.

Teva dropped its allegations of obviousness, and appealed to the Supreme Court of Canada. In a decision published on November 8, 2012, the Supreme Court held 7-0 that the patent was invalid for lack of proper disclosure. The Supreme Court considered the issues in the case “in light of the quid pro quo: Is the public getting what it ought to be getting in exchange for exclusive monopoly rights?”

The court first considered the issue of utility, and concluded that there was no question that the utility of sildenafil (the active component in Viagra) had been demonstrated in clinical studies (“Study 350”), as of the time of the filing of the patent application.

The court next turned to the issue of whether there was adequate disclosure in the patent so that a person of skill in the art could produce the claimed compound using only the instructions contained in the disclosure as required by §27 of the Canadian Patent Act. The court focused on the fact that at the time of filing, Pfizer had conducted tests that demonstrated that sildenafil was effective in treating erectile dysfunction (ED), but that none of the other compounds claimed in Pfizer’s Patent ‘446 had been shown to be effective in treating ED. The patent stated that one of the especially preferred claimed compounds was effective for treating ED, but did not disclose specifically which of the claimed compounds was the compound that was known to work.

The claims were structured as “cascading claims,” with Claim 1 involving over 260 quintillion compounds, Claims 2 to 5 involving smaller groups of compounds, and Claims 6 and 7 each reciting a single compound. Claim 7 recited sildenafil, the active component of Viagra, which was the only compound that had been shown to be effective in treating ED at the time of the invention.

The court concluded that Pfizer erred in not pointing out that sildenafil, the compound recited in Claim 7, was the preferred compound, stating that “the public’s right to proper disclosure was denied in this case, since the claims ended with two individually claimed compounds, thereby obscuring the true invention.” The court found that a person of skill in the art after reading the disclosure would have had to conduct further testing to determine which of the two individually claimed compounds was effective in treating ED. The court then held that the appropriate remedy was to invalidate Pfizer’s patent.

As a result of this ruling, and in response to the entry of generics for Viagra in the Canadian market, Pfizer reduced its price for Viagra in Canada. Generic versions of Viagra are not expected to go on sale in the United States until 2019.