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A staggeringly large number can be insufficient


 In his recent decision in Akebia Therapeutics, Inc v Fibrogen, Inc [2020] EWHC 866 (Pat), Lord Justice Arnold (sitting as a judge of the Patents Court) considered claims by Akebia for the revocation of six Fibrogen patents on the grounds of obviousness and insufficiency. The exclusive licensee under the patents, Astellas, in turn brought a cross-claim for threatened infringement.

The patents in suit concerned the use of HIF-PHIs, which are inhibitors of an enzyme known as hypoxia inducible factor-prolyl hydroxylase (HIF-PH), in drugs for the treatment of various types of anaemia and related conditions. Astellas hopes that the first oral HIF-PHI product will achieve blockbuster status by 2023.
In this article we focus on Arnold LJ's finding that five of the six patents were insufficient.

The law of insufficiency

A patent will be insufficient, and therefore invalid, if the specification does not disclose the invention clearly and completely enough for it to be performed by a person skilled in the art. Although a single ground of invalidity, insufficiency can be divided into three sub-categories:

  1. Classical insufficiency: where the invention cannot be performed at all without undue burden;  

  2. Excessive claim breadth: where the invention cannot be performed across the breadth of the claim without undue burden; and 

  3. Uncertainty: where the claim does not enable the skilled person to know whether they are within or outside of the claim.

In the present case, the patents in suit purported to protect what Arnold LJ agreed was a "staggeringly large" number of compounds. By way of example, Akebia's expert estimated that the following formula, found in one of the patents, could in some claims cover 10183 different compounds (that is, 1 followed by 183 zeros):

Formula (I)

 Akebia alleged that the patents in suit fell under the second and third types of insufficiency, and were therefore invalid.

Excessive claim breadth

At trial, Akebia relied upon evidence that the skilled medicinal chemist would have no reason for supposing or predicting that substantially all Formula (I) compounds would be effective in inhibiting HIF-PH or otherwise treating anaemia. There were also good reasons for believing that a significant number of Formula (I) compounds would not be effective.

Fibrogen, on the other hand, contended that Akebia's evidence was predicated upon either an incorrect construction of the claims or an incorrect understanding of the law. It argued that the claims were limited to compounds which worked, and it therefore necessarily followed that it was plausible that the invention would work across the scope of the claims.
Arnold did not accept Fibrogen's argument and considered that it was precluded by the decision of the Court of Appeal in Idenix v Gilead [2016] EWCA Civ 1089. In that case, claim 1 of the patent in suit was, on its face, a pure compound claim which embraced a very large number of compounds, but the court referred in its judgment to the parties' agreement that the claim should be construed only to cover compounds which had anti-viral activity. As the claim encompassed compounds which the skilled team would not have considered plausible had anti-viral activity, it was held to be insufficient.
In the present case, the claims in issue were implicitly promising that substantially all compounds which satisfied the structural definitions in the claims would have the claimed therapeutic efficacy, otherwise the skilled team would be presented with a choice between 10183 compounds in circumstances where the relevant specifications only disclosed five compounds which demonstrated efficacy. That would amount to no more than an invitation to the skilled team to find the other compounds covered by the claims which worked, and would mean that the patents did not sufficiently disclose the invention, as they would leave most of the work to the reader.
Fibrogen did not contend it was plausible that all, or even substantially all, of the claimed compounds had the claimed therapeutic efficacy, but instead argued that the technical contribution of the patents was the teaching that some of them could be used to treat anaemia.
However Arnold did not accept this argument, and held that the actual technical contribution to the art was no more than the identification of the five compounds listed in the specifications as having therapeutic efficacy. While that might justify a claim to a wider group of compounds that could plausibly be predicted to have similar efficacy, it did not begin to justify the claims in issue. Arnold also did not accept that the postulated technical contribution justified the breadth of the claims in issue – a finding that five compounds could be used to treat anaemia did not justify a claim to whichever ones out of 10183 compounds, in addition to those five, that the reader was able to find that worked, through his/her own research. He therefore concluded that claims in five of the six patents were insufficient for want of plausibility.
Arnold also made a finding of insufficiency based on the fact the invention could not be performed across the scope of the claims without undue burden, and that it would require a substantial research project to identify effective compounds other than the five specifically identified. While it was probable that the skilled medicinal chemist, if provided with sufficient resources, would be able to identify further effective compounds, they would not be able even in "many lifetimes of sustained effort" to make and test more than a tiny fraction of those compounds, and a substantial proportion either could not be made or would not work.


Arnold also found the certain claims insufficient for uncertainty. In Generics (UK) Ltd v Yeda Research & Developments Co Ltd [2012] EWHC 1848 (Pat), Arnold stated at [193] that “…it is necessary to distinguish between claims that are difficult to construe or that have a ‘fuzzy boundary’ … from claims that are truly ambiguous on the other. … If a claim is truly ambiguous, so that it is unclear what is the correct test to determine whether or not a product or process infringes, however, then the claim is insufficient…”
In the present case, Arnold accepted that claims which included the expression “structural mimetic of 2-oxoglutarate”, were insufficient on the ground of uncertainty. The skilled team would not know what constituted a “structural mimetic of 2-oxoglutarate”, and in particular what test to apply to distinguish between a compound which was, and a compound which was not, a “structural mimetic of 2-oxoglutarate”. Those claims were therefore uncertain and invalid for insufficiency.


It is clear from Arnold LJ's judgment that a claim which purports to protect a large set of compounds, whether by way of a general structural formula or otherwise, will be found insufficient if it is of excessive breadth. While certain claims in this case covered a "staggeringly large" 10183 compounds, the same principle will also apply to narrower claims, which cover significantly fewer compounds, if they are of excessive breadth.
Patentees have always needed to strike a balance between drafting claims which are broad enough to protect everything which they consider is covered by their invention, but not so broad that they exceed the technical contribution to the art. Arnold LJ's recent judgment will perhaps lead patentees to reconsider this balance and to draft their claims more narrowly to cover only what they plausibly predict will be effective, in order to avoid the risk of a finding of insufficiency and losing patent protection altogether.
This accords with the fundamental principle of patent law that the terms of a claim must be commensurate with, or be justified by, the patentee's technical contribution to the art. In other words, a patentee should not be able to claim a monopoly over something which it has not actually invested time and effort into inventing.

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