Patents: validity and infringement of broad formula claims

By Audrey Horton


The Patents Court has held that all but one of the claims of two families of patents were invalid for insufficiency as they lacked plausibility and could not be performed across their scope without undue burden, and that two claims were ambiguous or uncertain.


A patent is invalid for lack of inventive step if the invention claimed was obvious to a person skilled in the art having regard to the state of the art at the priority date (section 3, Patents Act 1977) (1977 Act). A patent application must disclose the invention sufficiently, clearly and completely for it to be carried out by a person skilled in the art, and the claims must be supported by the description (section 14, 1977 Act).

A patent for an invention is infringed by a person who keeps, disposes of, or offers to dispose of, any product obtained directly by means of the claimed process (direct infringement) (section 60(1)(c), 1977 Act). Indirect infringement occurs where an infringing invention is not put into effect by the defendant, but by someone who was supplied with means relating to an essential element of the invention for putting the invention into effect when he knows or it is obvious to a reasonable person in the circumstances that the means are suitable for putting and intended to put the invention into effect (section 60(2), 1977 Act).


F owned six patents relating to the use of enzyme inhibitors for treating anaemia. A applied to invalidate the patents to clear the way for their product, which was undergoing clinical trials. As well as alleging obviousness, A raised two insufficiency attacks against the patents: excessive claim breadth; and ambiguity or uncertainty.

F cross-claimed against A for threatened infringement. The patents were grouped into two families of three patents: family A; and family B.


The court held that all but one of the claims in both families were invalid, and that the only valid claim was not infringed on the basis of equivalence. It dismissed F's cross-claim and refused to grant an injunction as there was no present threat by A to infringe the family B patents.

The family A patents were not obvious but, apart from one claim, all other claims were invalid for insufficiency as they lacked plausibility and could not be performed across their scope without undue burden, and two claims were ambiguous or uncertain. The claims that were invalid for insufficiency would be infringed by A's product if they were valid.

All the claims in the family B patents were obvious and all but one claim was invalid for insufficiency. Even if the claims in issue were valid, there was no threat by A to infringe.

Lawyers instructing expert witnesses should ensure that the expert discloses all their previous relevant publications and, where appropriate, explains them in their report. While it can be advantageous to instruct expert witnesses in sequence, first asking them about common general knowledge, then finally revealing the patent, in order to avoid or reduce the risk of hindsight, there is no rule or principle that experts have to be instructed sequentially and there are often practical problems in doing so, for example if new prior art is introduced after the expert has read the patent. It is important to document everything that expert witnesses are shown at each stage. The preparation of a technical primer should also be regarded as mandatory in cases with a technical complexity unless there are good reasons to the contrary.

There is no principle of law that the skilled team is deemed to read all documents cited in a patent. It was a context- and fact-dependent question, depending on the wording of the specification and on the evidence. None of the documents cited in the specifications of the patents was expressly advanced as relevant to the sufficiency of the patents. Based on the texts of the patents and the expert evidence, the skilled team would not necessarily have followed up any of the cited publications.

A's insufficiency attack based on excessive claim breadth against the family A patents was that the relevant claims encompassed a very large number of compounds by reference to a general formula. The court rejected F's argument that the claims were limited to compounds which actually worked. Limiting the claims in that way did not provide plausibility because it implied that the patent was promising that substantially all compounds having the defined structure had the claimed therapeutic efficacy. As this was not supported by the specification, the patent did not sufficiently disclose the invention because it left the reader to find compounds which had the required activity. The finding that a few of the compounds worked was not a principle of general application across the breadth of the claims because the evidence showed that a large number of these compounds were not likely to work. The claims were therefore insufficient for lack of plausibility. The disclosure of the patent did not make it plausible that the invention would work across the whole scope of the claims.

The invention could also not be performed across the scope of the claims without undue burden, again rendering the claims insufficient. A substantial research project would be required to identify the claimed compounds which met the criteria for efficacy, aside from those specifically identified in the specification. As to the insufficiency attack based on uncertainty, the skilled team would not know what test to apply to distinguish between various compounds and so to know whether they were within or outside the claim, and as a result, these claims were invalid for uncertainty. As regards the family B patents, applying the same approach, all claims but one were insufficient due to excessive claim breadth and all claims insufficient due to uncertainty.

A's product did not infringe on a normal interpretation of the claim, as the structures of the two compounds differed. There was also no infringement by equivalence. A's product had a different structure and it had not been shown that it achieved substantially the same result in substantially the same way. Also, it was clear that the patentee intended that strict compliance was an essential requirement of the claim.

A intended to market its product in the UK but argued that the indications for which a marketing authorisation would be applied for would not infringe the family B patents which were limited by medical use. F had argued that there was threatened indirect infringement as it would be obvious to a reasonable person that A's product would be suitable for the infringing use. However, the clinical evidence did not suggest that it was likely that A's product would be used off-label in an infringing way.


This decision analyses a number of wide-ranging and topical validity and infringement issues in patent law. It shows the problem caused by drafting very broad claims on the basis of limited experimental evidence without explaining why the properties of the particular compounds which were studied should apply to all of the claimed broad class. Disclosure by the citation of a large number of papers and patents can only be used to overcome an insufficiency challenge to validity if there is a good reason on the face of the patent specification that the skilled person will study the documents and find the information without undue burden.

Case: Akebia Therapeutics Inc v Fibrogen, Inc [2020] EWHC 866 (Pat).

First published in the June issue of PLC Magazine and reproduced with the kind permission of the publishers.  Subscription enquiries 020 7202 1200