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Kim O'Connell
John Cusick
James Lawrence
The Full Court of the Federal Court has dismissed an appeal in Ranbaxy v Warner-Lambert, 1 revoking Warner-Lambert’s 2 patent for an isolated enantiomer of the cholesterol-inhibiting drug atorvastatin calcium but found that Ranbaxy’s product would infringe Warner-Lambert’s earlier patent covering the racemic mixture of the drug.
Cholesterol inhibitors and their chemistry
Atorvastatin calcium is sold in Australia and around the world under the brand name ‘Lipitor’ and is the highest selling prescription drug in the world. It is part of a class of chemical compounds called ‘statins’, which lower the presence of cholesterol in blood.
Atorvastatin calcium is a chiral compound that exists in distinct mirror image forms (like a pair of hands) that cannot be superimposed on each other. These mirror image forms are called enantiomers. Synthesis of chiral compounds ordinarily results in a mixture of equal amounts of right-hand (R) and left-hand (S) enantiomers, called a ‘racemic mixture’ or a ‘racemate’.
The patents
Warner-Lambert obtained one patent for the atorvastatin calcium racemate in 1987 (“Broader Patent”) and one for the isolated R-enantiomer in 1990 (“Enantiomer Patent”). In support of the application for the new Enantiomer Patent, Warner-Lambert had asserted that the isolated R-enantiomer was 10 times more active than the racemic mixture. Further, the specification of the Enantiomer Patent stated that it was “unexpectedly found that the enantiomer having the R form of [the drug] provides surprising inhibition of the biosynthesis of cholesterol”.
Decision at trial
Ranbaxy issued proceedings in 2004 seeking to revoke the Enantiomer Patent on the following grounds:
- the patent was obtained on a false suggestion or misrepresentation
- the invention was not useful, and
- isolating one enantiomer is not a patentable invention as it is not a manner of manufacture.
Warner-Lambert cross-claimed seeking an injunction to restrain infringement of both Patents. The trial judge, Young J, ordered that the Enantiomer Patent be revoked on the basis of false suggestion and utility, but rejected the argument that the isolation of an enantiomer was not a manner of manufacture. He found, however, that the Broader Patent would be infringed by Ranbaxy’s product.
Full Court findings
On appeal, the Full Court upheld Young J’s finding that the Enantiomer Patent was invalid because Warner-Lambert had (a) falsely suggested (and misrepresented) in the patent specification that the R-enantiomer alone had the unexpected and surprising level of potency of more than twice that of the racemate and (b) correspondence from Warner-Lambert’s patent attorneys to the Patent Office suggesting that the enantiomer alone was 10 times more active than the racemate was a false and misleading representation. Indeed, the Court found that it was expected that an isolated active enantiomer would have approximately twice the potency of the racemate.
Importantly, the Full Court affirmed the position that if a misrepresentation materially contributed to the Commissioner’s decision to grant a patent, even if other circumstances played a part in that decision, the patent can be regarded has having been obtained by a false suggestion or misrepresentation. Given the finding on false suggestion, the Full Court did not need to consider the grounds of manner of manufacture or utility.
Interestingly, the Full Court noted that Ranbaxy had abandoned the grounds of novelty and inventive step as part of its validity attack on the enantiomer patent. In its approval of the trial judge’s construction of the Broader Patent (in that it covered the racemate and each enantiomer separately), the Full Court said that “it may have been possible to argue that the invention of the Enantiomer Patent is not novel, in the light of the Broader Patent”. However, the Full Court was not required to decide this point as it was not an issue on appeal.
Although the decision in this case focussed on the unusual representations made to the Patent Office, the comments made suggest that there may be other grounds to invalidate an enantiomer patent where there is an earlier racemate patent. It is clear that each case must be considered in the light of the compounds concerned and all the attendant circumstances.
The Full Court also found that importation by Ranbaxy of a drug containing only one enantiomer infringed the Broader Patent on the basis that when properly construed, the claims of the Broader Patent included not only the racemate but each enantiomer individually.
Footnotes
1. [2008] FCAFC 82
2. Warner Lambert is part of the Pfizer group of companies.