In principal, the selection of a chemical compound from a previously identified class of related compounds can be inventive and, therefore, patentable if the selection is both unobvious and advantageous.

In the Matter of I.G. Farbenindustrie A.G.'s Patents, (1930) 47 R.P.C. 283 the Court refers to three general propositions that must be satisfied to create a valid selection patent. Firstly, the patent must disclose a substantial advantage to be secured by the selected members (or conversely the avoidance of a substantial disadvantage); secondly, all of the selected members must possess the claimed advantage; and, thirdly, the selection must be in respect of a quality of a special character that is peculiar to the selected group.

In Pfizer Canada Inc. and Warner-Lambert Company, LLC ("Pfizer") v. Minister of Health and Apotex Inc. ("Apotex"), 2008 FC 13, the validity of a selection patent was at issue. Pfizer sought an order prohibiting the Minister of Health from issuing a Notice of Compliance (NOC) to Apotex, until the expiry of Canadian Patent No. 2,021,546 ('546 Patent). Pfizer asserted that the '546 Patent was a valid selection patent which would be infringed if Apotex was permitted to produce the protected compound, atorvastatin calcium (marketed as LIPITOR). Apotex, in turn, contended that the '546 Patent was invalid on several grounds including double patenting and the absence of a valid selection.

Two related Canadian patents were at issue: Canadian Patent 1,268,768 ('768 Patent), and Canadian Patent No. 2,021,546 ('546 Patent). The application that led to the '768 Patent was filed in Canada on May 7, 1987, issued on May 8, 1990 and recently expired on May 8, 2007.

The '768 Patent is a genus patent that claims a class of compounds known as statins, which act to reduce cholesterol. The '768 Patent also claims pharmaceutically acceptable salts of the compounds, the individual enantiomers as well as racemic mixtures of the compounds. In particular, the patent covers the racemic mixture of atorvastatin.

Several years after the '768 Patent application was filed, Pfizer filed a related patent application that issued as the '546 Patent. The '546 Patent claimed a narrow subclass of the compounds previously described in the '768 Patent based on a claimed unexpected advantage. One of the compounds taught by the claims of the '546 Patent is atorvastatin calcium, which is a salt. Atorvastatin is the medicinal ingredient in the anti-cholesterol drug LIPITOR.

The '546 Patent application was filed in Canada on July 19, 1990, and will expire on July 19, 2010. Accordingly, if found to be valid, the '546 Patent would provide an additional three years of protection to Pfizer for LIPITOR, which, according to Pfizer, is the best-selling drug in history.

The "unexpected" finding of the '546 Patent, asserted by Pfizer, was the "surprising inhibition of the biosynthesis of cholesterol" provided by atorvastatin beyond what would have been anticipated from the prior art including the '768 Patent. The '768 Patent teaches a two-fold increase in inhibitory activity for the claimed compounds over the racemate of atorvastatin.

Pfizer relied upon internal experimental data to support the promises of the '546 Patent. Apotex challenged the reliability of Pfizer's data and pointed to other research findings which, Apotex said, taught away from those promises.

In the specification of the '546 Patent, Pfizer disclosed data that pointed to in vitro experiments indicating a ten-fold increase in inhibitory activity for atorvastatin over the racemate. The Court found that it is implicit in the findings cited in the '546 Patent that the supposed unexpected efficacy of atorvastatin in vitro would result in substantially increased efficacy beyond the benefits already promised by the '768 Patent which included the expected two-fold advantage of atorvastatin over the racemate.

Apotex attacked the reliability of the data in the '546 Patent not only on the actual results obtained but also on the basis of the scientific methodology used.

The evidence did not unfold in Pfizer's favour. Pfizer had to rely on hearsay evidence to interpret the obvious ambiguities and inconsistent language in the laboratory technician's notes from 18 years before the hearing.

The Court opined that Pfizer selected suspect data to support a dubious claim of a ten-fold advantage and drew an inference that Pfizer did not conduct further experimentation because it believed that well-controlled assays would not support its assertion of a surprising and unexpected finding for atorvastatin.

As a result, the Court rejected unequivocally the reliability of the data selected and relied upon by Pfizer to support the claim of a ten-fold advantage for atorvastatin calcium and found instead that the experiment was unreliable and the data it produced scientifically invalid. The Court found that the assay data relied upon by Pfizer was wholly unreliable and failed to establish any level of activity for atorvastatin beyond what a person skilled in the art would have expected to see, that is, no more than a two-fold advantage.

It followed that the Court declared the '546 Patent invalid because it does not meet the test for a valid selection and because it is objectionable for claiming subject matter already monopolized by the '768 Patent.

The case is instructive for two reasons. First, it reminds us of the importance of keeping accurate and complete laboratory notes and documentation detailing the experiments leading to any discovery. Secondly, the case reaffirms that a valid selection requires more than a bare assertion of "advantages"; what is required is a clear description of the special advantage or characteristic that supports the choice made over the other members of the class.