MORRISVILLE, NC (TheStreet) -- An experimental drug from Furiex Pharmaceuticals (FURX) produced more "consistent" stool and reduced pain compared to a placebo in two large, phase III studies of patients diagnosed with a form of irritable bowel syndrome that causes excessive diarrhea, the company said Tuesday.

Furiex shares soared at Tuesday's open, rising 147% to $113.94.

Furiex will submit the drug, eluxadoline, for U.S. approval at the end of the second quarter based on the positive results from the two studies. A European approval filing will likely be submitted in 2015.

Eluxadoline is designed to work like the opioid painkiller oxycodone except with low oral bioavailability and only in the gut, where it can treat diarrhea and reduce pain without causing constipation.

Furiex conducted two identical phase III studies which enrolled 2,428 patients with diarrhea-predominant irritable bowel syndrome (IBS-d). The primary endpoint of the studies was a composite response which required patients to report both improvement in stool consistency and reductions in abdominal pain.

FDA mandated that Furiex demonstrate a treatment benefit favoring eluxadoline over placebo for 12 weeks, while European regulators wanted to see a treatment benefit lasting 26 weeks.

In the first study, IBS-d patients treated with two different doses of eluxadoline -- 75 mg and 100 mg -- both responded better than placebo at 12 and 26 weeks. The benefit favoring eluxadoline was statistically significant.

In the second study, both doses of eluxadoline were numerically and statistically superior to placebo at the FDA-mandated 12 week time point, but at 26 weeks, only the higher 100 mg dose of eluxadoline was better than placebo. The lower dose of Furiex's drug was numerically better than placebo but not by enough to reach statistical significance.

When data from the two studies were pooled together, the response rates of eluxadoline at both doses were better than placebo and statistically significant at 12 and 26 weeks.

When the composite endpoint was broken down into the two components, eluxadoline was shown to have a greater effect on stool consistency than pain reduction.

In a previous phase II study, eluxadoline was associated with several cases of pancreatitis. In the phase III studies reported Tuesday, "mild" pancreatitis was reported by five patients treated with the drug, or a rate of 0.3% across both studies. Three of the patients were frequent alcohol users, a fourth patient entered the trial with a known risk factor for pancreatitis and the fifth patient experienced transient sphincter of Oddi spasm, a known side effect of the opiate class of drugs.

In an interview Monday, Furiex Chairman Fred Eshelman said all the reports of pancreatitis in the studies were mild and resolved quickly once patients discontinued eluxadoline. The association of pancreatitis with eluxadoline is similar to other opioids, all of which are approved with warnings on their respective labels, he added.

Diarrhea-predominant IBS (IBS-d) affects about 15 million people in the U.S. and another 13 million people in Europe, Furiex says. A single drug, Lotronex, is currently approved by FDA only for women with IBS-d. Access to Lotronex is also restricted because of safety concerns. The drug is not approved in Europe.

Ironwood Pharmaceuticals (IRWD) - Get Report markets Linzess for patients with constipation-predominant IBS, which is considered a separate disease.

Furiex shares closed Monday at $45.97. The stock is up 38% over the past 12 months.

-- Reported by Adam Feuerstein in Boston.

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