Plausibility And Undue Burden: A New Look Insufficiency After FibroGen v Akebia

• Published date: 12 November 2021
• Subject Matter: Intellectual Property, Litigation, Mediation & Arbitration, Patent, Trials & Appeals & Compensation
• Law Firm: Dehns
• Author: Mr Paul Harris

FibroGen Inc. v Akebia Therapeutics Inc. and another company; Astellas Pharma Inc. v Akebia Therapeutics Inc. and other companies [2021] EWCA Civ 1279

What are the practical implications of this case?

If Arnold J's approach to insufficiency for want of plausibility had stood, it would have meant that pharmaceutical claims would have to enable substantially all of the compounds satisfying the structural definition as to the therapeutic efficacy. Equally, insufficiency for undue burden meant that the skilled team must be able to identify substantially all compounds covered by the claim without undue burden.

What the Birss LJ judgement does, is propose tests by which an invention, described using general terms, and which patent discloses a principle of general application, can reasonably be expected to work for anything falling within the scope of the claims. For plausibility (which the judge considers is best described as 'reasonable prediction') there is a three step test (although there is potentially a further, separate functional limitation in the first step namely, treatment of eg a disease). First, identify what falls within the scope of the claimed class; second, ask what is it intended to do; and third, whether it is possible to make a reasonable prediction the invention will work with substantially everything falling within the claimed scope. For undue burden, claims with a functional feature, or a mix of those and a structural feature, must make possible, without undue burden, the identification of compounds which satisfy the relevant test (eg treatment of a disease). It is not necessary to identify all or substantially all compounds that satisfy that test.

What was the background?

FibroGen owned two families of patents (A and B) relating to the treatment of anaemia associated with the kidney: Chronic Kidney Disease ('CKD' - family A) and Anaemia of Chronic Disease ('ACD' - family B). The A patents predated the B patents and constituted full prior art.

In family A the claims in issue comprised a heterocyclic carboxamide compound (selected from a named group), that inhibited hypoxia inducible factor (HIF) prolyl hydroxylase (PH) enzyme activity, in a medicament for increasing endogenous erythropoietin, in the prevention etc of anaemia associated with CKD. The family B patents had claims for the same compounds but were for treatment of ACD.

Akebia had a rival HIF-PH inhibitor (vadadustat), which was in clinical trials. They brought proceedings for...