Salix Pharmaceuticals, a maker of drugs for gastrointestinal disorders, said U.S. regulators won’t approve its Xifaxan for a form of irritable bowel syndrome, Bloomberg News reported.

The FDA will issue what’s known as a complete response letter for the added use of Xifaxan, Salix said in a statement. Company-funded research published in the New England Journal of Medicine in January showed Xifaxan, already cleared for traveler’s diarrhea and a rare brain disorder caused by liver failure, helped ease irritable bowel symptoms such as abdominal pain and diarrhea.

“I wouldn’t ever call an FDA action a slam dunk, but certainly expectations were sky high,” said Corey Davis, an analyst with Jefferies & Co. in an e-mail. “There have been very few drugs I can think of that had a publication in NEJM and then subsequently never received FDA approval. Salix got sucker punched by the FDA.”

An FDA decision had been expected by March 7 for the new use of Xifaxan as a remedy for non-constipation irritable bowel syndrome, Salix said. Instead, Salix said regulators indicated the expanded use “is not ready for approval primarily due to a newly expressed need for retreatment.”

If Salix is required to conduct a new trial for repeat dosing of its drug, it would cost tens of millions and take years to complete, Davis said. The company said it would consider next steps once it receives the FDA’s letter.

At least 30 million people in the U.S. suffer from irritable bowel syndrome, and the most common symptom is diarrhea, said Mark Pimentel, lead author of the research reported from January. Most patients are treated with antidepressants, fiber supplements or diet and lifestyle changes, he said. Xifaxan, if approved to combat the syndrome, may help patients who don’t have constipation, he said.

The drug could be the first “that is treating a causative factor in irritable bowel syndrome,” said Pimentel, director of the GI Motility Program at Cedars-Sinai Medical Center in Los Angeles.