The U.S. Supreme Court turned away a bid by Alvogen's subsidiary Norwich Pharmaceuticals to sell a generic version of Canada-based Bausch Health's blockbuster diarrhea drug Xifaxan.

The justices declined to hear an appeal by Norwich Pharmaceuticals of a lower court's ruling that its proposed generic would infringe patents owned by Bausch unit Salix Pharmaceuticals for using Xifaxan to treat the liver-related brain disorder hepatic encephalopathy. In doing so, the justices let the lower court's ruling stand.

Xifaxan has been approved by the FDA to treat traveler's diarrhea and irritable bowel syndrome and can also be used to prevent hepatic encephalopathy. Bausch earned more than $1.8 billion from Xifaxan sales in 2023, according to a company filing with the U.S. Securities and Exchange Commission.

Bausch has separately agreed to allow Xifaxan generics from Teva Pharmaceuticals, Sun Pharmaceuticals and Sandoz starting in 2028 after settling related patent disputes.

Salix in 2020 sued New York state-based Norwich over its proposed generic of Xifaxan. A Delaware federal judge decided in 2022 that the generic would infringe three Salix patents related to treating hepatic encephalopathy while declaring other Salix patents invalid.

Norwich asked the patent-focused U.S. Court of Appeals for the Federal Circuit to reverse the judge's decision to block its generic. The Federal Circuit affirmed the decision in April.

Norwich in a filing told the Supreme Court that the patents did not cover Xifaxan uses for which Norwich had sought FDA approval.

"The cost of the delay in generic alternatives will be borne by patients and the healthcare system that will pay monopoly prices" for treatments that are "either not covered by a valid patent or that are covered by patents that would have been proven invalid or not infringed by a generic alternative," Norwich said in the filing.

Bausch did not respond to Norwich's Supreme Court petition.