An inventive selection can be made from a class of two or from a class of thousands. How­ever, the size of the class of compounds claimed in the genus patent is a factor to consider in determining whether a selection was obvious (see Eli Lilly Canada Inc. v. Apotex Inc., 2007 FC 455, 58 C.P.R. (4th) 353, at para. 306). The size of the genus may also impact the question of sound prediction and whe­ther the identified advantage of the selection would be unexpected.

In GlaxoSmithKline Inc. v. Pharma­science Inc., 2008 FC 593, the genus patent covered a virtually infinite number of compounds that had been identified as having an improved water solubility compared with a known antiviral drug, namely acyclovir, for the treatment of a variety of herpes and other viral infections.

In the selection patent, valacyclovir, one of the compounds identified in the genus patent, was claimed. The discovery asserted by the inventors was that valacyclovir surprisingly has improved bioavailability after oral administration compared with the compounds claimed in the genus patent. The specification also stated that, while acyclovir possessed a potent antiviral activity, it was known to be poorly soluble in water and poorly absorbed in the gastro­intestinal tract. The inventors ack­now­ledged the utility of the compounds claimed in the genus patent in solving the solu­bility problem of acyclovir but, by inference at least, they maintained that its oral bioavailability limitations were still unresolved. The specification further indicated that the bioavailability was measured by determining the absorption from the gut after oral administration in rats. As compared to two other compounds in the genus, the inventors found that valacyclovir is especially preferred by virtue of its particularly good absorption from the gut.

The Applications Judge was satisfied on the evidence presented that the bioavailability advantage that was asserted as the inventive selection was neither anticipated nor obvious. The Judge also accepted that improving the aqueous solu­bility of acyclovir in order to make aqueous formulations to inject or to use as eyedrops is vastly different from improving oral bioavailability of a drug.

However, the Applications Judge noted that in order to establish that a compound has a particular advantage over the genus from which it was chosen requires that the advantage not be found or be predicted to be found in a large number of members of the genus. The selected species must have an advantage over the class as a whole.

As the utility of valacyclovir as an antiviral prodrug had already been asserted in the genus patent, the specific utility of valacyclovir had to be found not in its antiviral properties or in improved solubility but in its supposedly better oral bioavailability profile over the other members of the class from which it was selected. That utility had to be established either by testing or by sound prediction or both. If the utility of valacyclovir for enhanced oral bioavailability over the genus compounds was not scientifically demonstrated or soundly predicted as of the Canadian filing date, the selection patent must fail for lack of utility (see Aventis Pharma Inc. v. Apotex, 2006 FCA 64). The fact that later evidence may establish utility does not transform the earlier speculation into something inventive.

The Applications Judge concluded that the inventor did not meet the burden of establishing a valid selection, at least in terms of utility. The Judge characterized the evidence as showing that valacyclovir had surprisingly improved bioavailability after oral administration compared with the two other compounds tested. However, there was no evidence to support the claim that valacyclovir has a unique bioavailability advantage over a few, some, many, most or all of the other ester compounds claimed by the genus patent. No explanation was provided as to why the test compounds were chosen or whether they would be expected to exhibit bioavailability properties commensurate with the thousands of other ester compounds claimed by the genus patent.

In a pharmaceutical selection patent, the invention is the discovery of a surprising or unexpected advantage of the selection over the genus of compounds from which it was chosen. The utility of such a selection is not found in the fact that it works to successfully treat some human condition or ailment but rather that it works surprisingly better than the compounds monopolized by the genus patent. That is the inventive promise made and the inventive promise that must be established.

In the end, the genus patent was found to be invalid for lack of utility because the patentee failed to establish an inventive selection by failing to prove a special advantage or utility vis-à-vis the genus from which valacyclovir was chosen.

The Applications Judge noted that he did not mean to suggest that a patentee of a selection patent must test every compound in the genus, but rather that it requires sufficient representative testing that a person skilled in the art could soundly predict that the surprising characteristic would not be expected to be found in a large number of the other members of the genus. In some cases, it may be possible to make such a prediction on the basis of the prior art but the patentee must at least offer evidence of a line of sound reasoning to show that the asserted advantage is special or peculiar to the selection.

While this result leaves the door open for selection patents, it remains to be determined what is meant by "sufficient representative testing" in order to validate a selection patent.