On 12 July, 2017 an important judgement was handed down by the UK Supreme Court in the case of Eli Lilly v Actavis UK. The court found that Actavis UK directly infringed Eli Lilly’s EP(UK) patent for pemetrexed disodium. The reasoning in the decision is significant for UK law in two legal areas: file wrapper estoppel and doctrine of equivalents.
The Court reasoned that there are situations where patent prosecution history may be relevant when considering infringement and that the UK courts should adopt a sceptical, but not absolutist, attitude to suggestions of referring to the contents of a patent prosecution file.
File Wrapper Estoppel
The use of patent prosecution history when assessing claims of infringement has been widely discouraged in the UK to date. However, in this decision the Court provided two non-exhaustive examples where patent prosecution history may be relevant when considering whether a variant infringes a patent:
(i) the point at issue is truly unclear if one confines oneself to the specification and claims of the patent, and the contents of the file unambiguously resolve the point, or
(ii) it would be contrary to the public interest for the contents of the file to be ignored.
More generally, the Court states that UK courts should adopt a sceptical, but not absolutist, attitude to suggestions of referring to the contents of a patent prosecution file.
Doctrine of Equivalents
Previously, Catnic  RPC 183 instructed the ‘purposive construction’ of claims when assessing infringement. This meant interpreting the language of the claim from the view of the skilled person rather than simply taking the ‘literal’ meaning. This meant that variants not covered by the ‘literal’ interpretation of the claim were nevertheless found to infringe because the skilled person would realise that the patentee intended such a variant to fall within the claims.
To provide guidance when departing from the ‘literal’ meaning of words in a claim to consider a variant, the Improver/Protocol questions were formulated. Subsequently, Kirin-Amgen  RPC 9 set out that ‘purposive construction’ must be always be used when applying the questions as are they not a substitute for trying to understand what the skilled person would have understood the patentee to mean by the language of the claims.
In the present decision, the Court found that something beyond the ‘normal’ interpretation of the claims can result in infringement. In the reasoning, it is said that two issues must be first addressed through the eyes of the skilled person when considering the infringement of claims:
(i) Does the item in question infringe any of the claims as a matter of “normal” interpretation; and if not
(ii) Although the item may be characterised as a variant, does it nonetheless infringe because it varies from the invention in a way which is immaterial?
When answering question 2, the Court reformulated the Improver/Protocol questions. Below is a comparison of the previous questions and the reformulated questions:
The Court added that issue (ii) involves not only identifying what the words of a claim would mean to the skilled person, but also considering the extent (if any) to which the scope of protection afforded by the claim should extend beyond that meaning.
This is a significant departure from the preceding case law where anything outside what the words of a claim would mean to the skilled person was considered to be outside the scope of protection.
File wrapper estoppel and doctrine of equivalents are now confirmed to exist in UK patent law. The increased likelihood of a UK Court turning to the patent prosecution history to settle an infringement case may lead to increased caution during European and UK patent prosecution.
The effect of adding a doctrine of equivalents approach to infringement in the UK is likely to have a big impact in the field of chemistry and pharmaceuticals. In this case, a claim relating to use of a disodium salt in the manufacture of a medicament for use in a therapy was found to be infringed by different salts beyond the scope of the claim. This is because the second reformulated question now retrospectively imbues the skilled person with the knowledge that the variant works at the priority date. The skilled person now only needs to consider whether it is obvious that the variant works in substantially the same way. This sets a new precedent for interpreting chemical formulae beyond the precise definitions given in a claim.
See the judgement Eli Lilly v Actavis UK  UKSC 48