Introduction

Plausibility is a concept that finds no mention in the European Patent Convention (EPC) or in the Patents Act 1977 (UK) (UK Patents Act). Nevertheless, as Lord Justice Arnold observed in this case (Nugee and Warby LLJ, agreeing), Sandoz v BMS, plausibility is a concept that has, over the past thirty years, “come increasingly to the fore in discussions of validity”: [1].

In Europe and the UK, a lack of plausibility arises when a specification asserts that the claimed product or process will solve a particular problem or produce a particular outcome, but there is not enough information in the specification to make it at least plausible to the skilled reader that the claimed invention will do so. A lack of plausibility means the claimed invention makes no “technical contribution” to the art (because no problem is solved) and is both lacking an inventive step and insufficiently disclosed. In Sandoz v BMS, Arnold LJ observed that “it makes no difference to the outcome whether the issue is viewed as one of inventive step or one of sufficiency”. It also does not appear to matter that the claim does not include, as an integer, the asserted outcome or advantage over the art.

Plausibility is not mentioned in the Australian Patents Act 1990 (Cth) (AU Patents Act) but has recently found its way into Australian jurisprudence at least with respect to the disclosure obligation in section 40(2)(a). Australian Courts have accepted that UK and European jurisprudence with respect to “classical insufficiency” should guide the approach to section 40(2)(a) of the AU Patents Act since its amendment by the Intellectual Property Laws Amendment (Raising the Bar) Act 2012 (Cth): Merck Sharp & Dohme Corporation v Wyeth LLC (No 3) [2020] FCA 1477 at [544]; Jusand Nominees Pty Ltd v Rattlejack Innovations Pty Ltd [2022] FCA 540 at [360]. The same has been said for “Biogen insufficiency” in the UK and the support requirement in section 40(3) of the AU Patents Act: Merck at [544]; Jusand at [369]. Whether plausibility is relevant in Australia, will be explored below. For pre-Raising the Bar patents, the concept is irrelevant.

Facts

Returning to Sandoz v BMS, the claims of the patent in suit (BMS’ patent) related to a compound called apixaban, marketed by BMS under the trade mark Eliquis, which is used to treat thromboembolic disorders. Apixaban’s use in therapy depends on its activity as a factor Xa inhibitor. However, the claim itself was to the compound per se, without limitation to its ability to treat those disorders or inhibit factor Xa.

At least insofar as the appeal was concerned, it was not in dispute that apixaban has proven to be a potent factor Xa inhibitor and a useful therapeutic for thromboembolic disorders, but Sandoz contended that the claim was invalid because the specification as filed did not make it plausible that apixaban would have any useful factor Xa inhibitory activity. That knowledge came later, after the application for the patent was filed, and was not disclosed in the application as filed.

The closest prior art disclosed embodiments which embraced apixaban, but there was no individual disclosure of that compound. Nor did the prior art make it obvious that apixaban would be likely to be efficacious as a factor Xa inhibitor.

It was common general knowledge that, for a factor Xa inhibitor to be potentially useful in treating thromboembolic disorders, it would need to have Ki/IC50 values in the nanomolar (nM) range and that 1-10 μM (micromolar, much larger than nanomolar) was not a good enough level of potency (it was too high).

The application for the patent in suit asserted under the heading “utility” that the compounds of the invention were inhibitors of factor Xa and were useful as anticoagulants for the treatment or prevention of thromboembolic disorders. It went on to say that the effectiveness of the disclosed class of compounds as factor Xa inhibitors “was determined” by means of the same chromogenic assay as disclosed in the closest prior art and that a Ki/IC50 <10 μM was sufficient. The application did not identify apixaban in particular as having a Ki/IC50 of less than 10 μM.

BMS did not assert that the skilled team reading the patent application with the benefit of their common general knowledge would interpret it as disclosing that apixaban had been tested and found to have nm Ki/IC50. BMS argued that the reader of the patent application would see something of potential value by working from what was described in the specification that apixaban was the key compound and that it was the one likely tested and, encouraged by that but having no data, would test apixaban and find that it had nanomolar Kis.

UK inventive step, sufficiency and the role of “plausibility” in both

Article 52(1) of the EPC provides that European patents “shall be granted for any inventions” provided that (among other things) they “involve an inventive step”. Article 56 provides that an invention “shall be considered as involving an inventive step if, having regard to the state of the art, it is not obvious to a person skilled in the art”.

Article 83 of the EPC requires that an application for a European patent “ disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art”. This is known as the “sufficiency” requirement and finds its equivalent in section 40(2)(a) of the AU Patents Act. Article 84 of the EPC requires, among other things, that the claims shall be “supported by the description”. This is known as the “support” requirement and finds its equivalent in section 40(3) of the AU Patents Act.

Article 138(1) of the EPC provides that a European patent may be revoked with effect for a contracting State by the courts of that State on grounds that include lack of patentability under Article 56 and failure to comply with Article 83. There is no ground of invalidity for failure to comply with Article 84 (unlike section 40(3) of the AU Patents Act). Sections 1(1)(a), 3, 14(3) and 72(1) of the UK Patents Act give effect in the UK to Articles 52(1), 56, 83 and 138(1) of the EPC.

Lord Justice Arnold observed that the criterion of plausibility, while not mentioned in any of these provisions, has been developed through the case law, initially of the Boards of Appeal of the EPO and latterly of the courts of the contracting States, including the UK. The general principle is premised on the policy that the extent of the patent monopoly should correspond to and be justified by the technical contribution to the art. That principle has been “applied in relation to the extent of the patent protection that was justified by reference to the requirements of Articles 83 and 84 EPC”: T939/92 Agrevo/Triazoles [1996] EPOR 171 at [2.4.2]. Therefore, the support and sufficiency requirements in the EPC are said to justify the plausibility criterion (although, as noted above support is not a ground of invalidity in the EPO or UK).

In Agrevo, it was said that “the same legal principle also governs the decision that is required to be made under Article 56 EPC, for everything falling within a valid claim has to be inventive.” That is, in the UK and Europe, a claim will not be “inventive” if the claim does not correspond to the technical contribution to the art, a question which does not appear to arise under any presently formulated Australian test for inventive step.

In Agrevo it was observed that, “if the claimed compounds were to be assumed not to have any technically useful property, then it could be postulated that the technical problem which is solved by the claimed compounds (or, in other words, the technical result achieved by them, on the basis of which the question of inventive step has to be decided), would be the minimalist one in such a situation, namely the mere provision of further (or alternative) chemical compounds as such, regardless of their likely useful properties”: at [2.5].

So, for example, if the claim is to specific compounds per se and the patentee does not assert the technical contribution is more than the provision of such compounds, then obviousness will be tested on that footing. In Agrevo, the patent applicant argued that, even on the basis of known starting compounds and known synthetic methods, the skilled person would have faced an unlimited number of possibilities for solving the problem of the “provision of further (or alternative) chemical compounds as such, regardless of their likely useful properties”. The applicant argued that a particular selection from that unlimited number was inventive, even if it was arbitrary, unless there was a direct pointer to the preparation of the claimed compounds in the prior art. The Board rejected that argument, observing that:

2.5.3 … The answer to the question as to what a person skilled in the art would have done depends on the result he wished to obtain, as explained in point 2.4.2 above. If this result is only to be seen in obtaining further chemical compounds, then all known chemical compounds are equally suitable as the starting point for structural modification, and no inventive skill needs to be exercised in selecting, for instance, the compound of formula XIV of [prior art citation] D3 for this purpose. Consequently, all structurally similar chemical compounds, irrespective of their number, that a skilled person would expect, in the light of the cited prior art, to be capable of being synthesised, are equally suitable candidates for solving such a hypothetical ‘technical problem’ to the skilled person, and would therefore all be equally ‘suggested’ to the skilled person. It follows from these considerations that a mere arbitrary choice from this host of possible solutions of such a ‘technical problem’ cannot involve an inventive step ... In other words, the Board holds that, in view of the underlying general legal principle set out in point 2.4.2 above, the selection of such compounds, in order to be patentable, must not be arbitrary but must be justified by a hitherto unknown technical effect which is caused by those structural features which distinguish the claimed compounds from the numerous other compounds. ...

2.5.4 It follows directly from these considerations that a technical effect which justifies the selection of the claimed compounds must be one which can be fairly assumed to be produced by substantially all the selected compounds.

The Board considered that the technical contribution to the art in that case was not the provision of a compounds per se as claimed but was to be discerned from the patent specification, which asserted the claimed compounds could achieve herbicidal activity. The Board said that, in deciding whether the claimed invention complied with Article 56 (inventive step), that technical problem could only considered if “it would be credible that substantially all claimed compounds possessed this activity”. The application did not make it plausible to the skilled person that all the claimed compounds had that herbicidal activity. Therefore, the Board concluded that the claims did not have an inventive step.

A recurrent issue in the other cases considered by Arnold LJ was whether the patent applicant could rely upon “post-published” evidence (i.e., evidence of technical effect post-dating the filing of the application for the patent) as demonstrating or supporting a technical effect asserted in the application. Ultimately, those cases held that post-published evidence could be used, but in such a narrow way that, to the authors’ minds, it is practically irrelevant to the question of plausibility. [CC1] [TC2] For example, in Warner-Lambert Co LLC v Generics (UK) Ltd [2018] UKSC 56 at [40], Lord Sumption observed that:

This does not mean that subsequent data is never admissible in a dispute about sufficiency, but the purpose for which it is admitted is strictly limited. Where the asserted therapeutic effect is plausible in the light of the disclosure in the patent, subsequent data may sometimes be admissible either to confirm that or else to refute a challenger’s contention that it does not actually work... But it cannot be a substitute for sufficient disclosure in the specification.

In this regard, an important recent case considered by Arnold LJ was the Board of Appeal decision in Case G 2/21 (not yet reported, 23 March 2023). In that case, the Board explained the limited way that “post-published evidence” could be used at [77]:

In order to meet the requirement that the disclosure of the invention be sufficiently clear and complete for it to be carried out by the person skilled in the art, the proof of a claimed therapeutic effect has to be provided in the application as filed, in particular if, in the absence of experimental data in the application as filed, it would not be credible to the skilled person that the therapeutic effect is achieved. A lack in this respect cannot be remedied by post-published evidence.

The Board at [92] also observed that plausibility “does not amount to a distinctive legal concept or a specific patent law requirement under the EPC, in particular under Article 56 and 83 EPC. It rather describes a generic catchword seized in the jurisprudence of the boards of appeal, by some national courts and by users of the European patent system.”

The authorities reviewed by Arnold LJ also made clear that plausibility did not require proof that the claimed invention would provide the technical effect, only that sufficient information is given in the application, in light of the common general knowledge, to make it plausible or credible to the person skilled in the relevant art that the technical effect would be achieved. This means experimental data is not necessary (though it no doubt is useful) to establish plausibility, especially in the absence of any “formulated substantiated doubt”. All that is required to be disclosed is “reasonable scientific grounds … for expecting that it might well work”: Warner-Lambert Co LLC v Generics (UK) Ltd [2018] UKSC 56 at [37] per Lord Sumption, but see also Lord Mance at [195].

The appeal

The trial judge found that the claimed invention lacked an inventive step and was insufficiently described because the skilled person would not consider from reading the patent application that the particular drug claimed, apixaban, had been tested for its factor Xa inhibitory activity: “Since there is no plausibility of any meaningful factor Xa binding the Patent is invalid.”

BMS contended that the trial judge was wrong because the claim was to a single (limited) compound and so the question of plausibility did not arise. BMS asserted that plausibility was concerned with overly broad claims and a single compound claim was necessarily confined and not over-reaching. Arnold LJ disagreed, holding:

Furthermore, the underlying principles are applicable as much to claims to single chemical compounds as to claims to classes of compounds and second medical use claims. The fundamental principle is that the scope of the patent monopoly must be justified by the patentee’s technical contribution to the art. This remains so whether the scope of the claim is broad or narrow. Thus 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. Equally, when considering insufficiency it is necessary to consider whether the specification sufficiently discloses the claimed invention. 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. It follows that, in order for a claim to a single chemical compound to be patentable, the application must make it plausible, when read in the light of the skilled person’s common general knowledge, that the compound has the utility asserted for it. Moreover, it makes no difference whether the claim incorporates the use of the compound as a technical feature or whether the claim is simply to the compound per se and the assertion of utility is only to be found in the specification. This is because, as explained above, there is no invention in merely identifying a new chemical compound; invention can only lie in identifying its utility.

Arnold LJ concluded:

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. As Lord Sumption said [in Warner Lambert]at [40], subsequent data cannot be a substitute for sufficient disclosure in the specification.

The UK Court of Appeal has therefore confirmed that plausibility arises even for narrow claims. The person skilled in the art must conclude that it is credible that the claimed invention will give the asserted benefit/technical contribution, even if that benefit or technical contribution is not a limitation in the claim.

Plausibility in Australia

The authors consider it unlikely that the question of plausibility could arise on the question of inventive step in Australia on the present state of the law. While the Raising the Bar Act made obviousness a lower hurdle than previously, the amendments changed how prior art can be taken into account, rather than expanding the pre-existing tests for obviousness in Australia. There is no strict requirement in Australia for a patent to identify a problem and its solution in order to provide an inventive step. Whether, for example, a claim to a chemical molecule per se involves an inventive step in Australia will likely depend on whether a person skilled in the relevant art would be motivated in light of the common general knowledge and any prior art to make that compound for any reason, not whether the compound achieves the asserted technical contribution to the art set out in the specification.

Nevertheless, the Australian courts have, so far, followed UK and European judge made law in the application of the disclosure obligation in section 40(2)(a) and support requirement in section 40(3) of the AU Patents Act: Merck and Jusand above. While neither Merck nor Jusand dealt substantively with the question of plausibility, Justice Rofe in Jusand at [377] referred to a delegate of the Commissioner’s decision in Evolva SA [2017] APO 57 at [45] without apparent criticism. That decision accepted plausibility was relevant to section 40(2)(a). Similarly, Burley J set out the plausibility requirement from Evolva without criticism in Cytec Industries Inc v Nalco Company [2021] FCA 970 at [144] (though his Honour did not otherwise address the issue of plausibility).

Plausibility and priority date

An interesting side note to plausibility in the UK and Europe is that Arnold LJ in Sandoz v BMS held that it should be tested by reference to the patent application as filed, rather than any later amended version of the patent. This was because, as Arnold LJ put it, “if plausibility arose from something that was only in the Patent and not in the Application, the Patent would be invalid for added matter”: at [4] and [53]. It is not clear that the same could be said in Australia. While section 40 of the AU Patents Act has traditionally been tested as at the date of the filing of the complete specification, it appears that once an amendment is made to the complete specification, that can cure any section 40 invalidity. Then the question is whether, if the amendment was wrongly made, the priority date of the claim is shifted (AU Patents Act, section 114), not that the claims are invalid per se (although that may be the effect).

As a further aside, at least in the UK and Europe, it appears that plausibility is relevant to the question of priority date – a claimed invention which is not plausible in light of the information given in the priority document cannot enjoy the priority date of the priority document: See Illumina Cambridge Ltd v Latvia MGI Tech SIA & Ors [2021] EWCA Civ 1924 (Arnold LJ, Nugee and Warby LLJ agreeing).

Given the differences in the language of the law for priority date in Australia as compared to that in the UK and EPC, some doubt might exist as to whether the position would be the same in Australia. Nevertheless, it appears that Burley J in TCT Group Pty Ltd v Polaris IP Pty Ltd (2022) 170 IPR 313; [2022] FCA 1493 was willing to apply the law of sufficiency in the UK to the question of priority date in Australia, which would mean plausibility should apply (though Burley J did not deal with that question). Furthermore, a delegate of the Commissioner in Fisher v Toolgen Incorporated [2018] APO 65 at [110] and [111] considered that, despite the linguistic differences between the priority date provisions in Australia and those in the UK and EPC, the law in the UK and EPC on priority date could be followed in its entirety. That question is on appeal to the Federal Court, awaiting judgment of Justice Nicholas.