What’s plausible? The UK Court of Appeal revisits the ever shifting concept

On 4 May 2023, the Court of Appeal laid judgment in the case of Sandoz Limited v Bristol-Myers Squibb Holdings Ireland Unlimited Company; Teva Pharmaceuticals Industries Limited v Myers Squibb Holdings Ireland Unlimited Company [2023] EWCA Civ 472, considering for the first time the decision of the Supreme Court in Warner-Lambert.

The case concerned a patent (European Patent (UK) No. 1 427 415 entitled “Lactam-containing compounds and derivatives thereof as factor Xa inhibitors”), of which Bristol-Myers Squibb Holdings Ireland Unlimited Company (BMS) was the proprietor, which expired on 16 September 2022, and the subsequent SPC (UK Supplementary Protection Certificate No. SPC/GB11/042 based on the Patent), which expires on 19 May 2026. The claims of the patent relate to apixaban, a compound marketed by BMS under the trade mark Eliquis pursuant to a marketing authorisation granted on 20 May 2011.

The claimants Sandoz Limited (Sandoz) and Teva Pharmaceuticals Industries Limited (Teva) claimed that the patent, and therefore also the SPC, were invalid on the grounds that the specification did not make it plausible that apixaban would have any useful factor Xa inhibitory activity. Furthermore, due to this lack of plausibility, the proposition made no technical contribution to the art, lacked an inventive step and was insufficiently disclosed.

Key findings by the Court of Appeal

Firstly, it was identified that the standard of plausibility is not limited to second medical use patents. While it is common ground that the majority judgment in Warner-Lambert is binding on UK courts at least in cases involving claims to second medical uses, the fact that a patent covered different grounds would not justify the court in departing from Warner-Lambert.

If a case cannot be distinguished from Warner-Lambert, the criterion of plausibility must be applied when determining whether the claimed invention involves an inventive step and is sufficiently disclosed.

A fundamental principle of patent law is that the scope of the patent monopoly must be justified by the patentee’s technical contribution to the art. When considering inventive step it is necessary to consider what technical problem the claimed invention solves; if it is not plausible that the invention solves any technical problem then the patentee has made no technical contribution and the invention does not involve an inventive step.

Sufficiency is a characteristic of the disclosure. It is not enough that the patentee can prove that the product can reasonably be expected to work in the designated use, if the skilled person would not derive this from the teaching of the patent, and if it is not plausible that the invention solves any technical problem then the patentee has made no technical contribution and the specification does not disclose any invention.

The judgment held that standard of plausibility which should be applied is the standard adopted by the majority in Warner-Lambert. This corresponds to the “ab initio plausibility” test identified in T 116/18 Sumitomo/Insecticide compositions, 11 October 2021, which sets out that post-published evidence could be taken into account if, based on the information in the application and the skilled person’s common general knowledge, the skilled person would have considered the technical effect plausible. The standard espoused by the minority in Warner-Lambert, or some other “less strict” standard, should not be applied.

The Court of Appeal relied on the opinion of the Supreme Court in Warner-Lambert that an invention is not made plausible by a bare assertion or the disclosure of a mere possibility that it will work. An invention may be rendered plausible by a specification or disclosure of reasonable scientific grounds showing that this was worth trying for a reason, experimental data, or a priori reasoning. Although the disclosure need not definitively prove the assertion that the product works for the designated purpose, there must be something that would cause the skilled person to think that there was a reasonable prospect that the assertion would prove to be true.

In reinforcement of the Supreme Court’s decisions in Warner-Lambert, the Court of Appeal rejected the “encouragement-plus-ability-to-test” argument and held that it is not sufficient for the application to encourage the skilled person to carry out simple tests identified in the specification to confirm the efficacy of the claimed product, even if carrying out such tests would indeed show that the product is likely to be efficacious.

Looking to the Future

Although the Court of Appeal unanimously upheld the reasoning of the Supreme Court in the Warner-Lambert judgment, the law on plausibility cannot be considered settled in light of the upcoming Supreme Court appeal hearing of FibroGen Inc v Akebia Therapeutics. This matter will also consider the law of plausibility in relation to the fundamental concept of insufficiency.

Read more in our global trade secrets and patents series:

• The Unified Patent Court: emerging trends from the first nine months
• A changing landscape for AI patenting in the UK
• Standard Essential Patents: key developments for SEPs and FRAND commitments
• Supplementary Protection Certificates (SPCs): recent developments in EU case law
• The limitation of patents in ongoing revocation procedures in Spain
• Navigating the New Frontier: AI Patentability at the European Patent Office
• Global trade secrets update