In a surprising decision in Teva Canada Ltd. V. Pfizer Canada Inc. 2012 SCC 60, the Supreme Court of Canada has unanimously ruled that Pfizer's patent covering ViagraTM is invalid.

The decision paves the way for Teva and others to market generic versions of ViagraTM before the patent's 2014 expiry.

The ruling comes more than five years after Teva commenced proceedings under the Patented Medicines (Notice of Compliance) Regulations challenging Pfizer's patent. 

Teva initially alleged that Pfizer's patent was invalid for obviousness, lack of utility, and insufficiency of disclosure. However, the Federal Court found Teva's allegation unjustified and issued an Order prohibiting the Minister of Health from issuing a Notice of Compliance to Teva, preventing it from marketing a generic version of ViagraTM.

Teva then appealed to the Federal Court of Appeal, dropping the allegation of obviousness, but the appeal was dismissed. Teva appealed again - to the Supreme Court.

The Supreme Court unanimously found that Pfizer's patent did not meet the requirements for sufficiency of disclosure and was therefore invalid.

The patent related to use of sildenafil (the active compound in ViagraTM) and various other compounds for the treatment of erectile dysfunction (ED). Sildenafil was initially developed by Pfizer in the mid 1980's for the treatment of hypertension and angina.

The patent contained seven claims of progressively narrower scope. Claim 1 encompassed a staggering 260 quintrillion compounds, while claims 6 and 7 related to individual compounds. Claim 7 relates specifically to sildenafil.

Sildeafil had been shown to be effective in treating erectile disfunction prior to filing the patent application. None of the other claimed compounds had.

The patent specification stated that"one of the especially preferred compounds induces penile erection in impotent males", but did not identify that the compound was sildenafil. 

The Supreme Court held that for the disclosure of the specification to be sufficient it must enable the"public to make the same successful use of the invention as the inventor could at the time of the application". Pfizer's patent specification failed this test because it did not indicate that sildenafil was the effective compound. Expert evidence showed that, even if only claims 6 and 7 were considered, a person skilled in the art would not have known which the effective compound was. Further testing would have been required. 

The Court stated that"Pfizer gained benefit under the Act - exclusive monopoly rights - while withholding disclosure in spite of its disclosure obligations. As a matter of policy and sound statutory interpretation, patentees cannot be allowed to "game" the system this way."

Having concluded that the disclosure of the specification was insufficient, the Court ruled the patent invalid. This is somewhat surprising, considering that the case arose under the Patented Medicines (Notice of Compliance) Regulations. The typical remedy under these Regulations would be to simply allow the Minister of Health to issue a Notice of Compliance.

Pfizer is challenging the ruling on the basis that the Supreme Court did not have jurisdiction to invalidate the patent, but in the meantime the ruling is proving problematic. The Federal Court recently granted summary judgement to another generic drug manufacturer - Apotex - inApotex Inc. vPfizer Ireland Pharma, 2012 FC 1339 declaring Pfizer's patent invalid, as "no result is possible other than a finding that the '466 patent is invalid" in view of the Supreme Court's ruling.

Whatever the outcome of Pfizer's challenge, the decision provides a strong reminder of the obligation to fully disclose an invention in the specification, and the potentially dire consequences of withholding information. If Pfizer had disclosed that sildenafil was the compound that had worked, the case may well have been decided in its favour.