UK raises the threshold for plausibility – will Australia follow?


The UK Supreme Court has handed down its judgement in Warner-Lambert v Generics & Anr [2018] UKSC 56 in which the issue of plausibility was considered in-depth. The Supreme Court unanimously held that broad medical treatment claims were invalid, with the majority finding that the requirement of plausibility is not a low, threshold test. This approach is somewhat at odds with that adopted by the Australian Patent Office in Evolva SA [2017] APO 57, which relied upon earlier UK case law.


The UK Supreme Court recently delivered their decision on a long-running dispute between Pfizer (parent company of Warner-Lambert) and Generics (UK) Ltd (trading as Mylan) and Actavis Group. The dispute concerned the validity and infringement of Warner-Lambert’s patent which covered “second medical use” (Swiss-style claim) protection of the drug, pregabalin. Claim 1 and dependent claims 2 and 3 were principally relevant and are as follows:

  1. Use of (S)-3-(aminomethyl)-5-methylhexanoic acid or a pharmaceutically acceptable salt thereof for the preparation of a pharmaceutical composition for treating pain.
  2. Use according to Claim 1 wherein the pain is inflammatory pain.
  3. Use according to Claim 1 wherein the pain is neuropathic pain.

The patentability requirement of sufficiency (and the related concepts of enablement and plausibility) ensures that the monopoly granted by a patent extends only to that which could reasonably be said to be disclosed in the patent specification and no further. The sufficiency requirement is found in section 14(3) of the UK Patents Act 1977 which states “[t]he specification of an application shall disclose the invention in a manner which is clear enough and complete enough for the invention to be performed by a person skilled in the art.” A patent may be revoked on the grounds that the invention is insufficiently disclosed under section 72(1)(c).

Actavis marketed a pregabalin generic under the brand name “Lecaent”. In 2014, Actavis and Mylan separately sought revocation of Warner-Lambert’s patent on the grounds of insufficiency. Warner-Lambert commenced infringement proceedings against Actavis later in the same year. Arnold J of the High Court held claims 1 and 3 to be insufficient and that even if the claims are valid, they are deemed not infringed. It was further ruled that a post-trial amendment lodged by Warner-Lambert to limit the claims to valid subject matter would amount to an abuse of process and was thus rejected. Warner-Lambert’s appeal in 2015 was unsuccessful as, broadly, the Court of Appeal upheld the decision of the High Court.

The judgement of the Supreme Court was handed down on 14 November 2018 for which inter alia issues of insufficiency and infringement of Swiss-style claims were considered. Here, we will discuss the ruling on plausibility in detail.

The Supreme Court’s Decision

The Supreme Court unanimously agreed that it was implausible that pregabalin would be effective at treating any type of pain (claim 1) and all neuropathic pain (claim 3) including peripheral and central pain.

However, the Lords were split on their views of what the appropriate test for plausibility should be. The majority of the Supreme Court (Lord Sumption, Lord Reed and Lord Briggs) disagreed with the Court of Appeal’s statement that:

The EPO and domestic cases do, however, indicate that the requirement of plausibility is a low, threshold test. It is designed to prohibit speculative claiming, which would otherwise allow the armchair inventor a monopoly over a field of endeavour to which he has made no contribution. It is not designed to prohibit patents for good faith predictions which have some, albeit manifestly incomplete, basis. Such claims may turn out to be insufficient nonetheless if the prediction turns out to be untrue. A patent which accurately predicts that an invention will work is, however, not likely to be revoked on the ground that the prediction was based on the slimmest of evidence. Thus, the claims will easily be seen not to be speculative where the inventor provides a reasonably credible theory as to why the invention will or might work. The same is true where the data in the specification is such that the reader is encouraged to try the invention”.

Turning to some of the observations of the majority of the Supreme Court, it was stated by Lord Sumption:

Without some disclosure of how or why the known product can be expected to work in the new application, it would be possible to patent the manufacture of known compounds for the purpose of treating every conceivably relevant condition without having invented anything at all, in the hope that trial and error might in due course show that the product was efficacious in treating at least some of them…[t]he patentee must disclose some reason for regarding this assertion as “plausible”. (emphasis added); and

“The Court of Appeal’s statement of the effect of the plausibility test has already been quoted (para 20 above). They considered that the threshold was not only low, but that the test could be satisfied by a “prediction … based on the slimmest of evidence” or one based on material which was “manifestly incomplete”. Consistently with that approach, they considered (paras 40, 130) that the Board’s observations in SALK laid down no general principle. I respectfully disagree. The principle is that the specification must disclose some reason for supposing that the implied assertion of efficacy in the claim is true. Plausibility is not a distinct condition of validity with a life of its own, but a standard against which that must be demonstrated. Its adoption is a mitigation of the principle in favour of patentability. It reflects the practical difficulty of demonstrating therapeutic efficacy to any higher standard at the stage when the patent application must in practice be made. The test is relatively undemanding. But it cannot be deprived of all meaning or reduced, as Floyd LJ’s statement does, to little more than a test of good faith. Indeed, if the threshold were as low as he suggests, it would be unlikely to serve even the limited purpose that he assigns to it of barring speculative or armchair claims.” (emphasis added)

Applying the test for plausibility as Lord Sumption had described it, the majority were not satisfied that efficacy in peripheral neuropathic pain was plausible. Notably, Lord Sumption said:

“The question, it must be remembered, is not whether it is plausible but whether the specification discloses something that would make it so in the eyes of the skilled person.”

In contrast, the minority of the Supreme Court (Lord Hodge, with whom Lord Mance agreed) thought Lord Sumption has set the standard for plausibility too high. Lord Hodge said, “I do not interpret those principles as requiring the patentee to demonstrate within its patent a prima facie case of therapeutic efficacy”.

As explained by Lord Hodge:

“Adopting the lower standard of plausibility which the recent decisions support, I am inclined to think that Arnold J, who heard and analysed the expert evidence on this matter, including that of Professor Woolf, Dr Scadding and Professor Wood, did not err in his evaluation of that evidence when he concluded that Warner-Lambert had done just enough to satisfy the plausibility test in relation to peripheral neuropathic pain. The result of the rat paw formalin test demonstrated that pregabalin reduced inflammatory pain at phase 2. There was expert evidence which treated as credible the suggestion that the efficacy of pregabalin in reducing pain which that test revealed would not be confined to inflammatory pain and that the medication would also be effective in relation to peripheral neuropathic pain. As Arnold J stated (para 351), it was common general knowledge that central sensitisation was involved (at least as an amplifying mechanism) both in relation to inflammatory pain and in relation to peripheral neuropathic pain and that it played a role in the rat paw formalin test. The patent had not demonstrated that pregabalin had an effect on central sensitisation and a prima facie case had not been made out. But the plausibility test does not require that standard.” (emphasis added)

Nevertheless, Lords Hodge and Mance agreed with the majority that claim 3 did not satisfy the standard for plausibility in respect of the central neuropathic pain.

Implications for Australia

In Australia, since 15 April 2013 (Raising the Bar Amendment) a specification must disclose the invention in a clear enough and complete enough manner to enable performance by a person skilled in the relevant art (section 40(2)(a)).

According to the Explanatory Memorandum to the Intellectual Property Laws Amendment (Raising the Bar) Bill 2011 (Cth), the purpose of the change of law was to require enablement across the full width of the claims, while adopting language that is consistent with that used in other jurisdictions. The wording in section 40(2)(a) is similar to section 14(3) of the UK patents legislation and Article 83 of the European Patent Convention.  The intention is that paragraph 40(2)(a) be given, as close as is practicable, the same effect as the corresponding provisions of UK legislation and the European Patent Convention.

Although it is clear that Australian courts are not bound to follow UK or European legal precedent, the courts often seek guidance from the approach used and case law from UK and Europe. Since Parliament has explicitly indicated that the new enablement requirement is intended to align with UK law, it seems even more likely that the Australian Courts will consider UK case law on this topic carefully. While there have not been any Court decisions on the new enablement requirement in Australia yet, the Patent Office recently issued a decision in Evolva SA [2017] APO 57 (the Evolva decision) which considered the importance of plausibility and whether an invention would work across the scope of the claim.  In this regard, the Evolva decision agreed with the Court of Appeal’s interpretation that the requirement of plausibility is a low threshold test and may be based on the slimmest of evidence. The Evolva decision further drew reasoning from another UK decision (HGS v Eli Lilly & Co [2011] UKSC 51) where Lord Neuberger stated that in some cases a “reasonably creditable” claimed use or “educated guess” can suffice.

As noted above, the majority in the Supreme Court disagreed with the principle that plausibility is a “low, threshold test”.  Given the precedent established by the Australian Patent Office in following earlier UK law for plausibility and the statements to this effect in the Explanatory Memorandum, we would anticipate that an Australian court would carefully consider the Supreme Court’s decision, despite the Lords being split on the relevant test for plausibility.

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