Science in the Triangle

Salix Pharmaceuticals, a Morrisville company that specializes in gastrointestinal treatments, has seen its shares rise nearly 50 percent in the past two days.

Investors rushed to trade the stock after Salix announced results from two late-stage studies Monday that showed rifaximin works better than placebo in treating non-constipation irritable bowel syndrome. Salix sells rifaximin for traveler’s diarrhea under the name Xifaxan.

About 12 percent of Americans suffer from irritable bowel syndrome, which can cause abdominal pain, bloating, constipation and diarrhea. IBS is not considered life-threatening, but it is difficult to treat, making it one of the most expensive gastrointestinal diseases in the U.S., according to an analysis in Nature Reviews Drug Discovery.

A handful of IBS treatments are on the market, but patients and doctors have been looking for more choices with fewer side effect.

Rifaximin is an antibiotic with minor side effects, including headache and constipation, and has the potential to replace sales Salix has lost since the end of 2007, when generic competition started pummeling its biggest seller, Colazal.

The company expected it will request regulatory approval of rifaximin for non-constipation IBS, the most common form of the disease, by mid-2010. Salix projected that treatments for non-constipation IBS generate about $2.2 billion in annual sales.

Shares rose as high as $21.34 on Monday and started trading above $19 Wednesday. The stock dropped below $19 in November 2005.