In a recent High Court judgment handed down in the case of Actavis UK Ltd & Ors v Eli Lilly & Company  EWHC 1511 (Pat), it was held that Actavis would not infringe Lilly’s European patent EP1313508B by launching a generic pemetrexed product containing any one of the active ingredients pemetrexed diacid, dipotassium or ditromethamine. The claims of Lilly’s Patent, which is not due to expire until June 2021, are directed to use of pemetrexed disodium (an antifolate) in combination with vitamin B12 for the inhibition of tumour growth in mammals. In concluding that the claims of Lilly’s patent are not broad enough to encompass the pemetrexed salts used by Actavis, Mr Justice Arnold made some interesting observations concerning the extent to which the prosecution history of a patent can influence claim interpretation. These comments would appear significant for patentees and patent practitioners alike.
Pemetrexed disodium is a cancer treatment, which has been marketed by Lilly under the brand name Alimta since 2004. In these proceedings, Actavis sought declarations of non-infringement (DNIs) before the English High Court in relation to EP1313508B for the UK, French, Italian and Spanish designations. In awarding a DNI to Actavis in all four jurisdictions, Mr Justice Arnold addressed some complex issues regarding the laws applicable in such multijurisdictional disputes. However, the key issue at stake for the purposes of determining infringement was construction of the term “pemetrexed disodium” appearing in the medical use claims of Lilly’s patent.
In making the assessment, it was considered appropriate to use “the Improver questions”, which were initially set out in the case of Improver Corp v Remington Consumer Products Ltd  FSR 181, as an aid to determining claim scope with respect to variants.
These questions are as follows:
1. Does the variant have a material effect upon the way the invention works? If yes, the variant is outside the claim. If no?
2. Would this (i.e. that the variant had no material effect) have been obvious at the date of publication of the patent to a reader skilled in the art? If no, the variant is outside the scope of the claim. If yes?
3. Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention. If yes, the variant is outside the claim.
In considering the pemetrexed salts to be used in the generic products, it was agreed by the parties that none of these has a material effect upon the way the invention works. However, on the basis of expert evidence, it was concluded that this would not have been obvious to the skilled person and as such, the claims of Lilly’s patent did not extend to cover Actavis’ products. Notwithstanding the answer to Q.2, Mr Justice Arnold went on to consider the parties’ arguments with respect to Q.3, and in doing so agreed with Actavis that the fact that the claims were limited to pemetrexed disodium specifically, during prosecution, did influence interpretation of the claims under Q,3. In particular, it was noted that it was not possible for Lilly to pursue claims to use of “pemetrexed” before the EPO because such claims were rejected under Article 123(2) EPC for added matter. This followed from the fact that the patent referred only to “antifolates” generally, or the specific example, pemetrexed disodium.
Although Lilly tried to argue that validity was not at issue in the proceedings, Mr Justice Arnold made it clear that he did not consider this a barrier to considering the effect on validity of Lilly’s proposed construction. It was also noted at :
….there is no good reason why the court should shut its eyes to the story told by the prosecution file. On the contrary, consideration of the prosecution file may assist in ensuring that patentees do not abuse the system by accepting narrow claims during prosecution and then arguing for a broad construction of those claims for the purposes of infringement.
Interestingly, this judgment conflicts with the German judgment handed down in April by the Düsseldorf Regional Court, which concluded that the use of pemetrexed dipotassium would infringe claim 1 of the German designation of Lilly’s patent. Mr Justice Arnold identified a number of reasons why the judgments differ and in particular, it was noted that the German court did not have regard to the prosecution history and did not consider the consequences of its construction for the validity of the patent.
To conclude, it is accepted that the UK has no doctrine of prosecution history estoppel equivalent to “file wrapper estoppel” in the US. However, it follows from this judgment that careful consideration may need to be given to any concessions made during patent prosecution. To the extent that the prosecution history is taken into account, it is worth noting that any inconsistencies between pre-grant amendments and arguments as to claim scope set forth during post-grant proceedings may not be tolerated by the UK courts.
For further information, please contact Joanna Peak or your usual Boult Wade Tennant adviser.