PatentlyO writes on obviousness in Allergan v Sandoz (Fed. Cir. 2013) (see here). The relevant claim is:
A composition comprising about 0.2% timolol by weight and about 0.5% brimonidine by weight as the sole active agents, in a single composition.
The District Court found this to be nonobvious. On appeal the Federal Circuit reversed this finding. Timolol and brimonidine were sold at the claimed concentrations and a prior art reference taught serial administration of the two substances. The District Court focused on unpredictability and reasonable expectation of success and the factors the FDA took into account for approval decisions. The Federal Circuit disagreed with this emphasis.
However a claim which referred to administration twice a day was found to be nonobvious by the Federal Circuit (over administering three times a day) based on the fact there was no loss in efficacy. However there was a dissenting opinion where Judge Dyk felt this was a newly-discovered property of an obvious method.
I found this interesting because it shows the interplay between the prior art, reasonable expectation of success and resultant properties is complex, making obviousness (inventive step) difficult to predict.