Is escitalopram a patent for the ‘452’s discovery that it is more potent than citalopam?

The most favourable reading that can be given to the ‘452 patent, a reading some of the respondents dispute, is that escitalopram is about 1.6 times more potent than citalopram. Since it was well within the realm of possibility that more, and indeed sometimes all, of the desired biological activity of a racemate might rest within one enantiomer rather than in the other, the discovery that escitalopram may be more beneficial than citalopram is not surprising. Indeed, if all of the desired activity resided in escitalopram, it would only be twice as potent as citalopram, which is not sufficiently unexpected to serve as the basis of a selection patent (GlaxoSmithKline v. Pharmascience Inc., 2008 FC 593). Surprises arise outside this range. There is no indication that escitalopram has other desirable or surprising traits such as less toxicity or an unexpected and substantial increase in solubility, stability, handling properties, processability or in its side effects profile. Consequently, if escitalopram is a selection patent, it is invalid.