Patent Law Blog (Patently-O):: "In re Metoprolol Succinate Patent Litigation (Fed. Cir. 2007).
Astra holds the patent on Toprol-XL (Metoprolol succinate) and sued several generic ANDA filers. On summary judgment, a Missouri Federal court held Astra’s patent invalid for improper obvious-type double patenting and unenforceable. Astra appealed for inequitable conduct during prosecution.
Double-Patenting: A later patent claim will be invalid for obviousness-type double patenting if it is not patentably distinct from an earlier claim from a commonly-owned patent. This analysis involves construction of both sets of patent claims.
[T]he critical inquiry remains whether the claims in the [prior] application define an obvious variation of the invention claimed in the … patent [at issue].
Normally, obviousness-type double patenting is avoided by filing a terminal disclaimer. Here, however, a secret inventorship and ownership dispute prevented such action.
Invalidity affirmed."
