A patentee may defeat a presumption of prosecution history estoppel by showing that use of the element at issue in the accused infringing product was not foreseeable in the field of the invention at the time of the patentee's narrowing amendment.

The district court granted the accused infringer’s motion for summary judgment of noninfringement.  The Federal Circuit upheld the district court’s decision holding that the patentee did not overcome the presumption of prosecution history estoppel because it failed to show that use of the element at issue of the accused infringer’s product was unforeseeable at the time of the amendment to the patent claim.

The patent at issue claimed certain conjugated estrogen pharmaceutical compounds designed to help prevent degradation.  The claimed conjugated estrogens are extremely water-sensitive and susceptible to moisture degradation during storage.  The patentee developed a formulation of the invention that included a moisture barrier coating (“MBC”) to overcome this issue.  During prosecution, the patentee narrowed the independent claim of the patent to cover the composition with an MBC comprising ethylcellulose.  The patentee argued that the alleged infringer’s MBC formulation was unforeseeable and thus, prosecution history estoppel did not apply.  The district court held that the accused infringer’s MBC formulation was foreseeable and the patentee’s amendment barred it from claiming that the accused infringer’s product, which did not use an MBC comprising ethylcellulose, infringed its claims.

The Federal Circuit upheld the district court’s decision.  It ruled that the use of the alternative MBC in the alleged infringer’s compound was foreseeable, thus, the patentee could not use that argument to overcome the presumption of prosecution history estoppel.  The patentee was barred from asserting its infringement claim.

A copy of the opinion can be found here.