District of Delaware Finds Terms of Namenda XR® Patents Indefinite During Claim Construction

On January 5, 2016, Chief Judge Leonard P. Stark of the District of Delaware found the claim language of several patents covering Namenda XR®—Forest Laboratories, Inc.’s extended-release drug for treating Alzheimer’s-type dementia—indefinite. Forest Labs., Inc. et. al v. Teva Pharm. USA, Inc. et al., Civ. No. 14-cv-00121-LPS (D. Del. Jan. 5, 2016). Notably, the court rendered this decision as part of its claim construction ruling, and before trial.

Background. Forest and co-plaintiff Adamas Pharmaceuticals, Inc. sued seven defendants seeking to market generic versions of Namenda XR®. Six of these patents required the dosage forms to yield “a plasma memantine concentration profile, as measured in a single-dose human PK study, characterized by a change in memantine concentration as a function of time (dC/dT) that is less than 50% that of an immediate release dosage form comprising the same dose of memantine . . . .” The defendants, including Teva,[1] argued that this claim limitation was indefinite. As the defendants argued, the patents lacked a single human PK study; instead, only hypothetical data from PK-based computer simulations was presented. The defendants argued that the lack of human PK studies caused uncertainty when determining how a person of ordinary skill in the art would know whether a formulation of memantine infringes. Specifically, the patents do not identify an appropriate PK profile to use as a reference point for analyzing the dC/dT limitation. Following the claim construction proceedings, all but two defendants have settled, and only Teva and Apotex Corp. remain.

Ruling. The court found the 50% dC/dT claim limitation was indefinite. Relying in part on Nautilus v. Biosig Instruments, Inc., 134 S.Ct. 2120 (2014), Judge Stark found that a person of ordinary skill in the art would not know with reasonable certainty whether a formulation of memantine infringes the claims. The 50% dC/dT limitation is found in each of the six patents owned by Adamas. With these patents found invalid, only one patent remains to be litigated. Trial is scheduled to begin on February 16, 2016.

Implications. Many patents lack clarity defining the scope of the claims. As this case illustrates, a patent reciting an invention in theoretical terms, but claiming it in more practical and specific terms, may be indefinite where the claims fail to define the metes and bounds of the invention. In addition, this decision shows that, at least in certain situations, it may be appropriate to address indefiniteness at the claim construction stage, and before trial.


[1] Teva is represented by attorneys of Carlson Caspers.