Back in January 2015, Mr Justice Arnold ruled in favour of Gilead in Idenix Pharmaceuticals, Inc & Ors v Gilead Sciences, Inc & Ors [2014] EWHC 3916 (Pat), holding that the claims of Idenix’s patent that are alleged to be infringed are invalid. The patent in question (EP 1 523 489) concerns modified nucleoside prodrugs for treating flaviridae infections, in particular hepatitis C virus (HCV).

Gilead had a marketing authorisation for sofosbuvir (an HCV treatment). Idenix claimed that Gilead was infringing by keeping and disposing of sofosbuvir. Gilead successfully counterclaimed at first instance that the patent should be revoked for lack of novelty over an earlier patent application, that it lacks inventive step because it makes no technical contribution, and also that it is insufficient and contains added matter. This decision has today been upheld and the appeal dismissed by the Court of Appeal.

The Court of Appeal re-states what is now becoming a familiar principle when assessing obviousness in the Patents Court, that the claimed technical effect of the invention must be plausible in light of the teaching of the specification and the common general knowledge. Such technical effect cannot be established solely by post-published evidence. The Court also expressly states that plausibility is a common threshold step to obviousness and industrial applicability, and the patent also failed for insufficiency on the same ground. Summarising the principle, by citing the Supreme Court in Eli Lilly, the Court states that: “the patent must disclose a practical application for the claimed product and that a plausible or reasonably credible claimed use or even an educated guess as to such a use could be sufficient for that purpose. On the other hand, a merely speculative use does not suffice“.

The decision