In a unanimous decision, the Supreme Court of Canada has provided valuable guidance to patent agents and litigators as to how Canadian patents will be read and enforced (Teva Canada Limited v Pfizer Canada Inc, 2012 SCC 60).

The subject matter of the patent needs no introduction. Sildenafil is the active ingredient in VIAGRA, one of the world's best known pharmaceutical products. There is no mystery or uncertainty as to the reason VIAGRA is prescribed.

Pfizer’s patent, however, was not as clear as the reputation its product enjoyed. The Pfizer patent described a class of compounds useful for the treatment of erectile dysfunction. The patent's description did not specifically identify sildenafil as an effective medication, even though Pfizer's tests conducted before the priority date showed that only sildenafil was effective for this purpose.

Pfizer's patent included a number of "cascading" claims, which defined the subject matter of the patent monopoly. Claim 1 set out a general formula which could produce 260 quintillion possible compounds used to treat erectile dysfunction. Successive claims narrowed the range of compounds monopolized; claims 6 and 7 related to a single compound each. Claim 7 related to sildenafil. Throughout the proceedings, Pfizer was unable to explain why its patent was directed to a number of compounds and why, although Pfizer knew that claim 7 claimed the only compound shown to be effective, the patent did not identify it as such or indicate that the remaining compounds had not been shown to be effective.

Message 1: Canadian Patent Law Drives a Hard Bargain

The main issue on the appeal was whether Pfizer had disclosed its invention sufficiently in its patent. The Supreme Court reiterated that proper disclosure is at the heart of the patent bargain; it is what the public receives in exchange for suffering a monopoly.

The disclosure end of the bargain is codified in s. 27(3) of the Patent Act, which requires that the patent specification “correctly and fully describe the invention and its operation or use as contemplated by the inventor”. This, according to the Supreme Court, requires the patent to disclose the nature of the invention.

To determine the nature of the invention and whether disclosure is sufficient, the entire specification, including the claims, must be considered and must answer the familiar questions: What is the invention? How does it work?

But that does not end the inquiry. Once the monopoly period is over, a person skilled in the field of the invention must also be able to use the invention as successfully as the inventor could at the time of the patent application. To uphold the bargain, with respect to each invention in question, the description in the patent must enable the skilled person to produce the invention using only the instructions contained in the disclosure, and without even a minor research project.

If a disclosure falls short of these requirements: no deal. The invention will be deprived of patent protection as, the Supreme Court held, should be the fate of VIAGRA.

Message 2: E Pluribus, Unum: Out of Many Claims, One Invention

One of the more unexpected aspects of the decision was that the sufficiency of disclosure may—but will not necessarily—be considered on a claim-by-claim basis. In upholding the validity of the patent, the lower courts determined whether disclosure requirements had been met with respect to patent claims individually.

However, the Supreme Court held that this was the wrong approach. Rather, in assessing whether the disclosure requirements are met, the Court must consider the specification as a whole, including all of the claims; separate claims may not signify separate inventions. Section 58 of the Patent Act allows for a valid claim to survive despite one or more invalid claims, but this section applies only after the invalidity analysis, including whether disclosure requirements have been met.

The Supreme Court therefore rejected the proposition that where a valid claim exists, the consideration of disclosure requirements can be limited to that claim. Further, the proposition that each claim in a patent concerns a separate invention is contrary to the scheme of the Patent Act. As a result, the number of claims in a patent is not commensurate with the number of inventions. And whether a patent with several claims encompasses one or many inventions can be critical to its validity, as it was in this case.

Examining the specification as a whole, the Court found that sildenafil and the other compounds of the invention “were so linked as to form a single inventive concept in the patent at issue”. Further, the specification did not contain any information to support the view that sildenafil for the treatment of erectile dysfunction is a separate invention from the use of any of the other quintillions of claimed compounds for that same purpose.

Accordingly, viewed as a whole, the patent at issue contained only one invention: the use of the compounds of a defined class that are effective in treating erectile dysfunction. However, because Pfizer had known that only one compound was in fact effective at the time of filing, the Court deemed this knowledge to define the true invention—and held that Pfizer had failed to disclose it adequately.

Message 3: Playing Hard to Get is a Risky Strategy

The Court unequivocally stated that there was no requirement to disclose in the patent the demonstration of the utility of the invention; but in this case, it was at the patentee’s peril. The Supreme Court was influenced by, and showed disdain for, the apparent shell game Pfizer had played in failing to identify sildenafil as the effective compound among the quintillions in its patent.

The patent referred to a single “invention” throughout. It identified nine “especially preferred” compounds and specifically claimed just two. Pfizer had conducted tests that demonstrated that only sildenafil was effective in treating erectile dysfunction. This, according to the Court, should have been described in the patent to meet disclosure requirements.

The skilled person, having only the specification, could not put the invention into practice and needed to undertake a minor research project to determine what the true invention was.

The Supreme Court noted that Pfizer had chosen an opaque method of drafting its patent and failed to explain why it had elected to suppress information that sildenafil was the tested and useful compound. Gaming the system by enjoying exclusive monopoly rights while withholding disclosure was, “as as matter of policy and sound statutory interpretation”, fatal to the patent.

Coyness, apparently, has no place in patent drafting. There is risk involved in less-than-full disclosure, particularly where the inventors have demonstrated utility. As a result, where a preferred embodiment of an invention has been tested and shown to work to the exclusion of other embodiments, disclosing this information in the patent appears to be critical. It is not enough to specifically claim the preferred embodiment and leave the skilled person to determine which one it is.

Message 4: There is Danger at the Bottom of the Patent Cascade

In a cascade of claims, Pfizer claimed a series of uses of compounds to treat erectile dysfunction starting with a claim that encompassed quintillions, and ending with two claims for individual compounds, one of which was the active ingredient in VIAGRA.

In practice, many patents are written with cascading claims that end with a series of individual claims. To the relief of patent agents everywhere, the Court did not throw out the practice of drafting cascading claims. The Court was careful to state that use of cascading claims “does not necessarily interfere in every case with the public’s right to disclosure”. The Court observed that the broad claims at the top of the cascade that include inoperative compounds are simply deemed invalid—presumably on the basis of inutility. The skilled reader knows that “when a patent contains cascading claims, the useful claim will usually be the one at the end concerning an individual compound”.

Nevertheless, the Supreme Court held that where there were two individually claimed compounds, and it was known that one worked and the other did not, the true invention was obscured as the disclosure failed to state in clear terms what the invention was. The patent therefore failed to meet the disclosure requirement.

Patents with cascading claims are, therefore, susceptible to attack based on insufficient disclosure if the inventor's knowledge regarding utility or inutility of those individual claims is not disclosed. The Supreme Court has signaled heightened disclosure obligations for individually claimed inventions at the bottom of the cascade.

Message 5: Insufficiency is No Longer the Poor Step-Sibling of the Invalidity Trinity

Compared to anticipation, invalidity and inutility, insufficiency of disclosure has rarely been asserted successfully to invalidate patents or defend against infringement. The Supreme Court decision has, however, given this ground legitimacy and strength.

Although there is no express remedy for insufficient disclosure in the Patent Act, here, where the patent was found to encompass a single invention, failure of disclosure was said by the Supreme Court to have rendered the entire patent invalid. If there is no quid—proper disclosure—then there can be no quo—exclusive monopoly rights.

In the future, the insufficient disclosure ground is likely to be used (particularly against cascading patents) with greater frequency and success. This is especially so where utility has been demonstrated, but the demonstrated utility defines the invention in a manner not reflected in the patent description.

An earlier version of the article was published in SLAW.