Canadian Patent Act Amendments Introduce File Wrapper Estoppel

New amendments to the Canadian Patent Act deem a patent's Canadian prosecution history (the so-called file wrapper) material in litigation where claim construction is at issue. Specifically, the file wrapper can now be admitted into evidence to rebut a patentee's representations about patent claim construction.

The practical impact of these amendments is that a patentee has to be even more careful about making representations regarding the construction of patent claims during Canadian prosecution. Such representations may now return to haunt the patentee in the form of permissible rebuttal to any claim construction positions advanced in litigation.

This poses a great challenge and burden on patentees. Many Canadian patents are prosecuted on a budget, without an eye to eventual litigation, often by non-lawyers.