Salix Pharms., Ltd. v. Norwich Pharms. Inc
Authored by: Jeremy J. Gustrowsky
A recent appellate decision sheds light on the complex interplay between pharmaceutical patents, generic drug approvals, and the standards for proving a patent is “obvious” in light of prior research. The case involved Salix Pharmaceuticals, which holds patents covering certain uses and forms of the antibiotic rifaximin (marketed as Xifaxan®), and Norwich Pharmaceuticals, which sought to market a generic version. The court addressed whether Norwich’s proposed generic would infringe Salix’s patents and whether those patents were valid in the first place.
The court upheld the lower court’s finding that several Salix patents—specifically, those covering a 1,650 mg/day rifaximin dosage for irritable bowel syndrome with diarrhea (IBS-D) and a particular crystalline form of rifaximin (form β)—were invalid because they were “obvious” in light of existing scientific literature and clinical trial protocols. The judges found that prior studies and publications provided enough information that a skilled scientist would have been motivated to try the claimed dosages and forms, with a reasonable expectation of success. Notably, the court emphasized that absolute certainty is not required for a finding of obviousness; it is enough if the prior art points in the direction of the claimed invention.
However, the court also affirmed that Norwich’s original application to the FDA (an Abbreviated New Drug Application, or ANDA) did infringe other Salix patents related to treating hepatic encephalopathy (HE), another use for rifaximin. As a result, the court agreed that the FDA could not give final approval to Norwich’s generic until after those patents expire in 2029—even though Norwich later tried to amend its application to remove the infringing use. The court explained that simply amending an ANDA after judgment does not automatically entitle the applicant to immediate approval; the district court has discretion to decide whether to revisit its earlier decision.
This decision highlights the importance of robust prior art analysis in pharmaceutical patent cases and clarifies that courts can delay generic drug approvals when any part of an ANDA infringes a valid patent. It also signals that post-judgment amendments to generic applications may not be enough to sidestep a court’s prior ruling, especially if the applicant has already fully litigated the issue.