Canada - Patentability of Isomers

In March 2005 the Canadian Federal Court rejected the allegation of invalidity of Sanofi’s patent (the 777 patent). The 777 patent was directed to clopidogrel bisulfate (for the blood-thinner Plavix), which is a dextrorotatory isomer having improved properties over the corresponding levorotatory isomer. Sanofi-Aventis had brought suit against Apotex for selling a generic version of clopidogrel bisulfate in Canada.

Apotex alleged that the 777 patent was anticipated and obvious over a prior patent (the 875 patent) which disclosed the racemate (i.e., a substance containing equal amounts of the two isomers).

Apotex submitted that the 875 patent described the particular isomer but it was held that, given the 875 patent did not provide any teaching on how to separate the isomers from the racemate, the 777 patent was not anticipated. Furthermore, Apotex argued that the 875 patent described that the isomers may be separated and that with routine experimentation a person skilled in the art could obtain the dextrorotatory isomer and hence the 777 patent was rendered obvious.

However, this argument was rejected because there was no evidence that a person skilled in the art would have known the dextrorotatory isomer's properties were advantageous prior to separation and subsequent testing and that if a person skilled in the art would have to try various well known methods in order to discover which one would produce the desired result, this could not render the desired result obvious.