In order to be patentable an invention must show, amongst other things, the existence of an "inventive step". One way in which an opponent may seek to demonstrate a lack of inventive step is by showing that the apparently inventive step was in fact "obvious to try"; in other words, a person skilled in the art would think of undertaking that step and do so with some expectation of success. 

Quite what "obvious to try" means in practice is not clear but the Court of Appeal has recently provided some guidance in the case of Teva v Leo Pharma [1].

The patent in suit concerned an ointment to treat the skin condition, psoriasis. The treatment used two active ingredients each of which was already well-established for use in treating psoriasis but the two were not used together and indeed patients were warned that the two ingredients should not be used together. The reason why they could not be used together was that each required the use of a stabilising aqueous solvent. As one of the ingredients was acid and the other alkaline, the same solvent could not be used in each case.

The issue for researchers was whether a non-aqueous solvent might do the job so that an ointment could be produced which would use both the active ingredients. And, if so, which solvent? At trial the prior art in issue was for a patent using a non-aqueous solvent that was used as an anti-inflammatory steroid. Birss J found that, based upon this prior art, the idea of using the solvent in question as part of a research project was obvious.

The Court of Appeal disagreed, ruling that Birss J had set the hurdle for "obvious to try" too low. The Court of Appeal held that there was nothing about the prior art that made it a stand-out candidate to trial for the dual active ointment for the treatment of psoriasis. It was rather just one of a number of non-aqueous solvents that potentially might be worth exploring further. Simply because it was a non-aqueous solvent did not mean it would necessarily work.

The Court of Appeal's approach was anchored in the real world, where researchers are confronted with obstacles, deadlines, budgets and so on. It was also relevant that the problem addressed by the patent had existed for a number of years without a solution and Birss J, in the Court's opinion, had failed to address his mind to why the problem was not addressed before the patent in suit.