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Prosecution history no guide to claim construction

A recent decision by the Court of Appeal (Actavis UK Ltd. v Eli Lilly & Company) is of considerable interest to patent practitioners and their clients.

In the USA, there is a well-established legal doctrine that the statements and arguments of a patent applicant, made during the course of prosecuting the patent application before the US Patent and Trademark Office, have a binding effect and can be relied upon by others subsequently to help interpret (or “construe”) the scope of the patent claims ultimately granted.  Thus, if an applicant argues that a word in his claims should be interpreted in a narrow way (e.g. in order to avoid a piece of prior art), then he cannot later argue (for example, during infringement proceedings) that the word should be interpreted more broadly.  This doctrine is called “file wrapper estoppel” or “prosecution history estoppel”.

In the Actavis case mentioned above, the Court of Appeal considered whether, under English law, such estoppel exists in relation to the interpretation of patent claims.  The Court did not make a formal judgement on this point, but gave a clear indication that it considered the prosecution history of a patent application was NOT relevant to the correct construction of the claims, and indeed might rule such prosecution history evidence as inadmissible in the future.

Whilst the Court did explain the reasons for taking this view, it does mean that in the UK we are left with the unsatisfactory situation that a patent proprietor can argue that the same claim means different things, at different times.

This could make the claim scope more uncertain for third parties, but patent owners may have broader protection.  If you have any questions regarding this issue, please get in touch with your regular Nash Matthews contact.