Patent Claiming Salt of Cardiac Drug Held to be an Inventive Selection

Recently, in Pfizer Canada Inc v The Minister of Health and Ratiopharm Inc, 2006 FCA 214, the Canadian Federal Court of Appeal considered the issue whether an inventive selection existed in a patent which claimed the besylate salt of the cardiac drug amlodipine. Pfizer Canada Inc (Pfizer) had brought an application pursuant to the Patented Medicines (Notice of Compliance) Regulations for an Order prohibiting the Minister of Health from issuing a Notice of Compliance (NOC) to Ratiopharm Inc (Ratiopharm) for the drug amlodipine until after the expiration of Canadian Patent No 1,321,393 ("˜393 Patent). The "˜393 Patent claims an invention in the selection of the besylate salt of amlodipine from the class of pharmaceutically acceptable salts of this drug which were already known in the art. The disclosure of the "˜393 Patent stated that the besylate salt was selected because of its unusual combination of desirable properties when preparing pharmaceutical formulations. It is established law that the "inventive step in a selection patent lies in the discovery that one or more members of a previously known class of products possess some special advantage for a particular purpose which could not be predicted before the discovery was made" (Beecham Group Ltd v Bristol Laboratories International SA [1978] RPC 521). The Applications Judge considered this principle and held that the "˜393 Patent was not a valid selection patent on the basis that the research conducted by the patentee leading up to the selection amounted to mere "verification" that the besylate salt had certain desired formulation properties. However, the Federal Court of Appeal disagreed. According to the Court, verification involved confirming predicted or predictable qualities of known compounds (i.e., compounds that had already been discovered and made). In this case, however, all of the experts had admitted that the formulation properties of any salt of amlodipine could never have been expected but had to have been determined empirically. Since the properties of the salts had to be determined empirically, the Court held that the discovery of the besylate salt's special formulation properties was not mere verification but was an inventive selection. As a result, the decision of the Applications Judge was set aside and the Court prohibited the Minister from providing an NOC to Ratiopharm in respect of its proposed amlodipine besylate product until the expiry of the "˜393 Patent. For the Applications Judge's decision, visit: http://decisions.fct-cf.gc.ca/fct/2006/2006fc220.shtml For the Federal Court of Appeal decision, see: http://decisions.fca-caf.gc.ca/fca/2006/2006fca214.shtml Summary by: Nick Wong