One of the many highlights from the recent Court of Appeal decision in Fibrogen v Akebia is Birss LJ’s decision on insufficiency. Of particular interest is the test set out for assessing plausibility where a patent claims a principle of general application. The test is as follows:

i) what it is which falls within the scope of the claimed class?

ii) what it means to say that the invention works? In other words what is it for?

iii) is it possible to make a reasonable prediction the invention will work with substantially everything falling within the scope of the claim?

Birss LJ highlighted that when applying step (i) of the test, both the structural and functional features of the claims must be considered. He also confirmed that, when assessing step (iii), the existence of inactive compounds in a Markush formula is not fatal unless it undermines the reasonableness of the prediction - it is a matter of fact and degree.

The full decision can be found here.