A recent decision of the Court of Appeal (UK), namely Actavis UK Ltd & Ors v Eli Lilly & Company [2015] EWCA Civ 555 (25 June 2015), covered a lot of ground, including interpretation of Swiss-style use claims, direct and indirect infringement, and claim construction. However, it is the issue of admissibility of prosecution history that this commentary will focus on.
Since the UK House of Lords addressed the issue back in 2004 (Kirin-Amgen Inc & Ors v Hoechst Marion Roussel Ltd & Ors [2004] UKHL 46 (21 October 2004)), it was considered that the prosecution history should not be taken into account when construing (interpreting) claims.
However, in Actavis UK Ltd & Ors v Eli Lilly & Company [2014] EWHC 1511 (Pat) (15 May 2014), the Patents Court relied on the prosecution history to guide it in claim construction of an Eli Lilly patent, European Patent No. 1 313 508, with claims directed to a chemotherapeutic drug, pemetrexed disodium.
During the hearing, the parties put forward different assertions as to how a person skilled in the art would interpret the term ‘pemetrexed disodium’. All the chemists out there are probably wondering “How could there be multiple interpretations? Surely it’s just the disodium salt of pemetrexed?” Well, the patentee put forward the interpretation that ‘pemetrexed disodium’ covered any salt of pemetrexed that was pharmaceutically acceptable and sufficiently soluble. The Patents Court considered that reviewing the prosecution history might be of use in resolving cases where patent proprietors accepted a narrow interpretation of claim terms during prosecution, then argued for a broader interpretation during enforcement proceedings. Ultimately, the Court decided that the limitation to pemetrexed disodium during patent prosecution proceedings was sufficient to limit claim construction during the Court proceedings to the narrow interpretation, thus ‘pemetrexed disodium’ did not encompass equivalents.
In the most recent decision of the Court of Appeal, the use of the prosecution history as an aid to claim construction was rejected, thus returning to the general principle under UK law that the prosecution history is rarely useful when interpreting claims during post-grant proceedings.
It is interesting to contrast the issue of reference to prosecution history in the UK with that in Australia and the US.
Australian courts have not issued a decision on whether or not it is permissible to make reference to prosecution history when interpreting claims during post-grant proceedings. However, it is generally considered not possible to interpret a granted patent on the basis of amendments or arguments made during prosecution, based on an obiter dictum view of the Federal Court (Prestige Group (Aust) Pty Ltd v Dart Industries Incorporated (1990) 26 FCR 197).
This is in contrast to the well established doctrine of file wrapper estoppel in the US, where amendments and arguments made during prosecution can have a significant effect on claim construction and scope. Consequently, where a narrowing amendment has been made during prosecution of a patent application, the doctrine of file wrapper estoppel prevents the patentee from expanding the scope of a claim under the doctrine of equivalents to include integers that were abandoned by that narrowing amendment.
If you have any queries regarding the issues raised in this post, please do not hesitate to contact me by emailing bernadette.hawkins@spruson.com.