The main claim of the patent in issue was directed to a Markush group with, according to the opinion, 260 quintillion possible compounds. There was evidence that one of them, sildenafil, was effective for that purpose. The opinion records that none of the other compounds had been shown to be effective. Although test data was available to Pfizer and the specification indicated that tests had been carried out, the tests were not reported in the specification and sildenafil was not identified as the most promising compound.

As the opinion explains, sildenafil could not be considered in isolation from the other inactive compounds because the specification provided no basis for doing so:

“[66] In this case, if we consider the specification as a whole, there is nothing to support the view that the use of sildenafil for the treatment of ED is a separate invention from the use of any of the other claimed compounds for that same purpose. No specific attributes or characteristics are ascribed to sildenafil that would set it apart from the other compounds. Even if we take into consideration the fact that sildenafil is an “especially preferred compound”, there is still nothing that distinguishes it from the other eight “especially preferred compounds”. The use of sildenafil and the other compounds for the treatment of ED comprises one inventive concept.”

At para [76] the opinion explains:

Pfizer had the information needed to disclose the useful compound and chose not to release it. Even though Pfizer knew that the effective compound was sildenafil at the time it filed the application, it limited its description to the following statement:

“In man, certain especially preferred compounds have been tested orally in both single dose and multiple dose volunteer studies. Moreover, patient studies conducted thus far have confirmed that one of the especially preferred compounds induces penile erection in impotent males.”

It chose a method of drafting that failed to clearly set out what the invention was. Even now, in its factum to this Court, Pfizer offers no explanation as to why — knowing that Claim 7 contained the tested and thus, the useful, compound — it elected to withhold that information.

An inventor has a choice to disclose the invention or to keep it a trade secret, but if the disclosure route is followed then it is not possible simultaneously to disclose and conceal, as was established in a line of authorities form R. v Arkwright onwards. For that reason, in this instance, the patent did not stand up in court.