In a recent case before the UK Patents Court, Merck Sharp and Dohme Limited (MSD) has succeeded in its action for revocation against European patent 1422218B, owned by Shionogi & Co Limited. Shionogi alleged infringement of their patent by MSD’s product raltegravir, an anti-HIV therapy that has been on the market since 2007. MSD denied infringement and sought revocation. In finding the claims of the patent invalid for lack of inventive step and insufficiency, the judge reinforced the need to plausibly demonstrate therapeutic efficacy across the full scope of second medical use claims in order to achieve robust patent protection.

This latest decision follows a series of recent UK patent cases in which plausibility has been at the heart of the proceedings. These cases include: Actavis v Eli Lilly [2015] EWHC 3294 (Pat); Merck v Ono [2015] EWHC 2973 (Pat); Warner-Lambert Company LLC v Generics (UK) Ltd (t/a Mylan) & Ors [2016] EWCA Civ 1006. All of these cases highlight the need to match as closely as possible the scope of second medical use claims with the real contribution to the art, and in some cases, the value of experimental data in dictating the scope of patent protection possible. The claims of Shionogi’s patent were second medical use claims directed to compounds for preventing or treating a viral disease. The compounds were defined by a Markush formula and at trial, the formula was estimated by one of the experts to cover 10^39 compounds. This number dwarfs the total number of unique chemical substances ever registered by a factor of approximately 10^31.

MSD argued both lack of inventive step and insufficiency essentially on the basis that it was not plausible that substantially all of the compounds encompassed by the claims would possess the required therapeutic efficacy. In particular, it was noted that the claims were supported by experimental data for only 12 compounds. The judge, perhaps understandably, agreed that it was not plausible from the teaching of the patent that all of the 10^39 claimed compounds would possess the required therapeutic activity. In this regard, two things are notable.

First, the judge commented on the failure of the patent to elucidate the key structural features linked to the activity of the tested compounds. The lack of information concerning the pharmacophore was held to limit the patentee’s contribution to the field and consequently the monopoly to which they were entitled. Secondly, the judge agreed with the positon put forward by MSD that in order to demonstrate a likelihood of efficacy in preventing or treating viral disease, a simple biochemical enzyme inhibition assay was not enough. The compounds of the claims were intended as anti-viral drugs based on their ability to inhibit viral integrase, the enzyme responsible for incorporation of the viral genome into a host cell. However, it had been demonstrated prior to the filing date of the patent that not all integrase inhibitors possessed antiviral activity. On this basis, the judge concluded that it was not plausible from the biochemical in vitro data in the patent that the compounds would be efficacious as anti-viral drugs.

European patent 1422218B is also the subject of parallel opposition proceedings before the EPO and was maintained at first instance in amended form. The claims considered by the UK court in this recent case were the amended claims accepted by the Opposition division and therefore, it is of particular note that they have been found invalid in the UK. The case is due to be heard before the Technical Board of Appeal at the EPO and it will be interesting to see if the outcome is consistent with this UK decision.