US and UK law of patent enablement – clear divergence for now

On 15 December 2023, the pending appeal to the UK Supreme Court (“UKSC”) in the case of Fibrogen v Akebia was withdrawn. The UKSC had granted permission to appeal on 3 October 2022 from the decision of the Court of Appeal (“EWCA”) handed down in August 2021. That decision was itself an appeal from the decision of Arnold LJ sitting as a judge in the High Court (Patents Court) (“EWHC”) dated 20 April 2020.

Background and UK approach

The relevant claims were for a broad class of compounds, defined by structure and function, to be used for treating specified types of anaemia. Arnold LJ in the EWHC had held under a narrow approach that the claims were invalid for insufficiency as lacking plausibility and imposing an undue burden on the skilled addressee.

The EWCA overturned this decision and laid down a three-part test combining structural and functional aspects of the claim in the assessment of insufficiency. Essentially the EWCA held that a claim to a broad Markush class of structurally related compounds which inhibited enzyme X so as to treat disease Y had a narrower scope than previously understood. Birss LJ held that the claim only included within its scope those members of the Markush class of compounds which in fact inhibited enzyme X, rather than all of the members of the structural class. Then the relevant question for the skilled person was whether it was plausible that substantially all of the members of this narrower enzyme-inhibitory class would be effective to treat disease Y.

US approach

On 18 May 2023 the US Supreme Court (“SCOTUS”) handed down its decision in Amgen v Sanofi the most recent instalment of the global battle between Amgen and Sanofi over the cholesterol lowering drug Praluent. The Court upheld the decision of Federal Circuit Court of Appeals (“CAFC”), finding two of Amgen’s patents (US…