What does the Court of Appeal's ruling in FibroGen v Akebia mean for patentees and the law on insufficiency? | Fieldfisher
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What does the Court of Appeal's ruling in FibroGen v Akebia mean for patentees and the law on insufficiency?



United Kingdom

This blog looks at the Court of Appeal's decision in FibroGen v Akebia which could have implications for patentees, particularly those in the pharmaceutical industry.


The decision of the Court of Appeal in FibroGen Inc v Akebia Therapeutics Inc [2021] EWCA Civ 1279 CA (Civ Div) should come as welcome news for IP practitioners and pharmaceutical companies alike. The ruling overturns the previous decision of Lord Justice Arnold (sitting as a judge in the Patents Court), whose  approach some commentators considered set an unreasonably high threshold for patents claims which contain both structural and functional features in relation to a finding of insufficiency on the grounds of plausibility and undue burden.

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. (For a summary of the ruling of the Patents Court and a reminder of the law of insufficiency see our earlier blog: SnIPpets | Intellectual Property Law Blog | A staggeringly large number can be insufficient | Fieldfisher.)

The approach adopted by Birss LJ (who gave the principal judgment in the Court of Appeal) holds two key takeaways:
  1. That a finding of plausibility (which he termed as "reasonable prediction") should be ascertained by applying a three-step test (see below), as opposed to the single question asked by Arnold LJ in the High Court. In reframing the approach on how to evaluate sufficiency on the grounds of reasonable prediction, the judgment arguably strengthens the potency of patents that cover broad categories of chemical compounds; the breadth of the claim itself is perhaps now less likely to lead to invalidity issues.

  2. When assessing a claim with a functional feature (or with a mix of structural and functional features), it must be possible for the skilled person, without undue burden, to identify compounds which satisfy the relevant test, and to find out whether any sensible compound within the claim satisfies the test. However, as a matter of law, it is not necessary to establish that the skilled person can identify all or substantially all the compounds which satisfy that particular test.

Findings on plausibility

Referring in particular to the fourth principle identified by Kitchin LJ in Regeneron v Genentech [2013] EWCA Civ 93, Birss LJ confirmed that an invention can be defined using general terms, provided that it can reasonably be expected that the invention will work with anything falling within the scope of these terms. Put differently, any assertion that the invention will work across the scope of the claim must be credible or plausible.

In light of this assessment, Birss LJ outlined a three-part test for "reasonable prediction":
  1. Identify what it is that falls within the scope of the claimed class:

  2. Determine what it means to say that "the invention works"; i.e. what is the invention for? and

  3. Determine whether it is possible to make a reasonable prediction that the invention will work with substantially everything falling within the scope of the claim.

In applying this test, Birss LJ considered that Arnold LJ had not correctly identified the compounds falling within the claimed class, which he found to be an error of "principle and approach". He also confirmed that the invention's purpose was the treatment of a CKD form of anaemia.

Finally, he asked whether it was possible to make a reasonable prediction (that is to say, whether it was plausible) that compounds which satisfy both the structural and functional features of the claim will be useful in the treatment of CKD anaemia. On the facts, he held that this was a reasonable prediction, and consequently overturned the High Court's ruling on plausibility.

Findings on undue burden

Again reviewing Regeneron, Birss LJ considered Kitchin LJ's fifth principle: that it must still be possible to perform the invention across the scope of the claim without undue effort. He analysed the principle in line with the judgment of the German Supreme Court in Dipeptidyl-Peptidase-Inhibitoren BGH X ZB 8/12, from which he concluded that the proposition derived from EPO case law (and relied on by Arnold LJ) that a skilled person must be able to identify substantially all compounds covered by the claim without undue burden is – in principle – wrong.

Following this conclusion, the Court of Appeal held that in this case (although it might be a lot of work) a skilled team would be able to find some effective compounds within the claim without undue burden. However, this work should be "routine for a medicinal chemist and iterative nature". Consequently it overturned Arnold LJs finding of undue burden.


The Court of Appeal's ruling and approach to insufficiency is kinder to patentees than that of Arnold LJ’s in the first instance decision. The result is a positive one from an innovator's point of view, and pharmaceutical manufacturers can perhaps now have greater confidence in the potency of patents for broad chemical formulae, while at the same time patent drafters are given more clarity. However, there remains uncertainty about just how broad a class of compounds can be. How many compounds are too many compounds? What must we define as excessive? Is it only a "staggeringly large" group of compounds which fulfil this definition, or something else? We will have to wait and see!

With special thanks to Kurt Shead, Trainee, co-author of this blog. 

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