The doctrine of equivalents broadens the effective scope of a patent claim and is therefore undeniably pro-patentee. A major concern of third parties has been the potential for a patentee to argue in favour of the validity of a narrow claim and then seek to claim infringement of a much broader, and potentially invalid claim, under the doctrine of equivalents. Until now there has been little clarification from the courts on whether this apparent abuse of procedure would be sanctioned. This has left third parties with little confidence that a limitation required for reasons of validity should be considered a true limitation for the purposes of assessing infringement.

In Akebia Therapeutics Inc v Fibrogen, Inc the UK High Court has now confirmed that it is contradictory to limit a claim for reasons of validity and subsequently seek to rely upon the doctrine of equivalents to extend the scope of protection of that claim during infringement proceedings.

The doctrine of equivalents requires the court to ask the following questions when assessing infringement by an equivalent:

1. Notwithstanding that it is not within the literal meaning of the relevant claim(s) of the patent, does the variant achieve substantially the same result in substantially the same way as the invention, that is, the inventive concept revealed by the patent?
2. Would it be obvious to the person skilled in the art, reading the patent at the priority date, but knowing that the variant achieves substantially the same result as the invention, that it does so in substantially the same way as the invention?
3. Would such a reader of the patent have concluded that the patentee nonetheless intended that strict compliance with the literal meaning of the relevant claim(s) of the patent was an essential requirement of the invention?

In order for there to be deemed infringement under the doctrine of equivalents the answers to these questions need to be “yes”, “yes” and “no”.

The present case relates to the validity of six patents belonging to FibroGen, as Akebia Therapeutics, and Otsuka Pharmaceutical sought to clear the way for launch of their vadadustat product for the treatment of anaemia associated with chronic kidney disease (CKD). During the validity action the patentee had limited a number of claims to one specific chemical compound (compound C) for reasons of sufficiency. The patentee then argued that claims limited to compound C were infringed by vadadustat under the doctrine of equivalents.

Upon assessing infringement under the doctrine of equivalents the judge, Lord Justice Arnold, was easily able to determine that the first two questions should be answered negatively. This is primarily due to structural differences between compound C, other compounds disclosed in the patents, and vadadustat.

In spite of this conclusion, Lord Justice Arnold went on to consider the third question and it is here that we find some clarification of how the doctrine of equivalents could affect the interplay between validity and infringement.

Upon considering the third question, the High Court confirmed that limiting a claim to a specific compound for reasons of validity must be interpreted as “disclaiming the other ways of achieving the same effect disclosed in the specification” (paragraph 453). The decision also confirms that any generic statements made during prosecution to suggest that deleted subject-matter has not been abandoned or that the claims have been limited merely to expedite prosecution should not affect this conclusion.

The reasoning presented in the decision deviates from the conclusion reached in Actavis UK Ltd and others v Eli Lilly and Company for at least two reasons.

Firstly, the decision suggests that the reader of a patent would be aware of limitations required to achieve a valid claim. This appears to be contradictory to the conclusion in Actavis UK Ltd and others v Eli Lilly and Company that the file wrapper should be considered only in a very limited number of circumstances. It is however often the case that validity and infringement proceedings before the courts are combined, negating any need to consult the prosecution file wrapper to determine why certain claim amendments have been made.

Secondly, the present decision concludes that the reader would consider limitations made to achieve validity to require strict compliance with the literal meaning of the claim, answering question three positively and leading to a finding of non-infringement. This is in contrast to Actavis UK Ltd and others v Eli Lilly and Company, where limitation of the claims to avoid adding matter was not considered a reason for the reader to require strict compliance with the literal meaning of a claim. It may be that the two cases can be distinguished by the type of amendment required, since added matter is a formal ground whilst sufficiency is a fundamental requirement for patentability. Nevertheless, some uncertainty must be considered to remain.

Summary points

This decision provides some long overdue clarification of how the doctrine of equivalents will be applied by the UK courts.

On the face of it there appears to be some certainty for third parties, allaying the fear that a patentee will be permitted to make a limiting amendment for reasons of validity but to argue in favour of a broader claim when assessing infringement. However, third parties should take this conclusion with caution when determining whether an amendment is likely to be considered to require strict compliance with the wording of the claims. The reason for an amendment and the similarity of the potential infringement to subject-matter excluded from the claim by the amendment both appear to be important factors for consideration.

It is unlikely that we have seen the last decision clarifying interpretation of the doctrine of equivalents. In the coming years we may see further clarification of the circumstances in which amendments are considered true limitations for the purpose of assessing infringement. In the meantime, third parties would remain wise to interpret granted claims broadly when assessing freedom to operate.