Canada: Supreme Court Invalidates Pfizer’s Blockbuster VIAGRA® Patent

Last Updated: November 16 2012
Article by Sanjaya Mendis

Most Read Contributor in Canada, September 2018

Canada's top court has struck down Pfizer Inc.'s lucrative patent on VIAGRA, paving the way for generic entry into the Canadian marketplace shortly.

In Teva Canada Ltd. v. Pfizer Canada Inc., 2012 SCC 60, the Supreme Court of Canada unanimously (7-0) declared Pfizer's patent for its blockbuster VIAGRA drug invalid on the basis of insufficient disclosure.

Background – the '466 Patent

Pfizer research scientists initially investigated "sildenafil citrate" (VIAGRA's active compound) for use as a cardiovascular drug.  However, upon discovering sildenafil's peculiar effect on rats, scientists began to suspect that the compound might be useful in treating erectile dysfunction (ED).  This suspicion turned out to be correct, and Pfizer's blockbuster drug VIAGRA was invented.

Pfizer holds Canadian Patent No. 2,163,446 ('466 Patent) entitled "Pyrazolopyrimidinones for the treatment of impotence".  The '466 Patent consists of 7 cascading claims of successively smaller groups of compounds with claim 1 claiming 260 quintillion compounds, and then claims 6 and claim 7 relating to a single compound each. Claim 7 discloses sildenafil, the active compound shown to be effective in treating ED.

However, the '466 Patent did not specifically identify that sildenafil was the effective compound.  Rather, the specification contained statements such as "one of the especially preferred compounds induces penile erection in impotent males" and "certain especially preferred compounds have been tested".

Teva Canada Limited, one of Canada's largest generic pharmaceutical manufacturers, alleged that the '446 Patent's cryptic description of sildenafil was obscure and failed to properly meet the disclosure requirements under the Patent Act.

Insufficient Disclosure – Section 27(3)

Section 27(3) of the Patent Act lists the disclosure requirements for a patent, which among other things, requires that the specification "correctly and fully describe the invention".

The SCC reaffirmed that sufficiency of disclosure lies at the heart of the patent system, a basic policy rationale underlying the Patent Act:

The patent system is based on a "bargain", or quid pro quo:  the inventor is granted exclusive rights in a new and useful invention for a limited period in exchange for disclosure of the invention so that society can benefit from this knowledge.

In the case of Pfizer's '466 Patent, the SCC found Pfizer did not live up to its bargain, as the public's right to proper disclosure was denied in this case.  Writing for a unanimous bench (7-0), Justice LeBel held Pfizer's patent drafting strategy of referring to "certain especially preferred compounds" in the specification, without actually identifying sildenafil as the effective compound (despite Pfizer's knowledge of such), failed to clearly set out what the invention was.

Pfizer's election to withhold the identity of the active compound in the '466 Patent's specification resulted in the skilled person having to undertake a "minor research project" to determine whether the useful compound was disclosed in claim 6 or claim 7.  This caused the trial judge to remark the patent's disclosure "plays games with the reader":

Why did the disclosure not simply state that [the] compound in Claim 7 was sildenafil? The patent plays "hide and seek" with the reader. The reader is expected to look for the "needle in the haystack", or "the tree in the forest". Remember, Claim 1 is for a range of compounds which includes 260 quintillion compounds.

The SCC further ruled Pfizer's patent could not be saved by section 58, which does not allow a court to consider the validity of a single claim (i.e. claim 7), independently of the rest of the specification.

Sound Prediction

With respect to utility, the SCC noted all that is required is the invention described in the patent do what the patent says it will do.  The '446 Patent stated it would be useful in treating ED, which was true.  In addition, the Court held sound prediction was not an issue, and declined to address Teva's controversial and hotly-debated argument that there is an "enhanced" or "heightened" disclosure requirement with respect to sound predictions.

The Judgement

After succeeding at the Federal Court, and the Federal Court of Appeal, Pfizer has been dealt a costly blow by now losing before the SCC.  In addition to its market exclusivity period being truncated by two years (the '466 Patent was set to expire in 2014), Pfizer is also now on the hook for a protracted section 8 damages period to Teva for keeping Teva off the generic market.

The SCC's message was clear in that a patentee's disclosure obligations under the Patent Act are a fundamental principle underlying the patent system.  As a matter of policy, the SCC held that patentees will not "be allowed to 'game' the system".

Interestingly, the SCC declared the '446 Patent "void". This was a curious result because the Federal Court does not possess the jurisdiction to invalidate a patent in summary proceedings brought pursuant to the PM(NOC) Regulations, which was how Teva's case was brought.  It is unclear at this point whether this was an error by the SCC or intentional.  From the text of the decision, it appears this jurisdictional issue was not canvassed.

In the end, the SCC found Pfizer failed to live up its end of the quid pro quo of the Patent Bargain system – namely, getting exclusive monopoly rights to the VIAGRA patent without disclosing to the public that sildenafil was in fact the effective compound for treating ED.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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