Son, Never Compete in a Field with Existing Generics!!!
Home work? I am in the pharmaceutical sciences for about 20 years.
FYI: Regarding the strength of patent, Chemistry Entity Patent is the strongest, Use Patent may be useful, and Formulation Patent is usually the weakest. Dozens formulation patents were defied by generic challengers in the court every year.
Unfortunately, Namenda XR only has formulation patent.
BTW, I have a thought of that FRX may never launch Namenda XR (even they said "will launch in early 2013"). They may directly chase the FDC of N + D. A Combination Patent could be better than a Formulation patent.