The Salix Pharmaceuticals (Nasdaq:SLXP) irritable bowel syndrome drug candidate that failed to win U.S. Food and Drug Administration approval earlier this year is on its way to starting another phase 3 clinical trial.

The Raleigh-based company said an FDA advisory committee has accepted the company’s proposed clinical trial design studying Xifaxan for irritable bowel syndrome with diarrhea.

In declining to approve the drug, the FDA expressed concern that the earlier study did not adequately assess how patients responded to retreatment with the drug. Patients with IBS may need to retreat with additional doses to manage the chronic condition. In addition to questioning retreatment, FDA reviewers also questioned how long the treatment lasts. Reviewers concluded that Xifaxan’s effect lasts for the first four weeks of treatment, then diminishes.

Clinical trial enrollment is set to start in January. Salix estimates it will take about two years to complete trials, resubmit a response to the FDA complete response letter and receive an approval decision.

Salix said the proposed design addresses points raised by the FDA in the March complete response letter. The primary objective of the study is to evaluate Xifaxan’s efficacy in patients who responded to initial treatment with the drug. Salix will now work with the FDA to finalize the protocol for a multi-center, randomized, double-blind, placebo-controlled trial with IBS patients.

Bill Forbes, Salix’s executive vice president, medical, research and development, said in a statement that the company is pleased with the advisory committee’s support of the study design.

“Over the past several months Salix and the FDA have worked collaboratively to develop a study proposal intended to collect prospective controlled data to support the repeat use of rifaximin in IBS with diarrhea following the recrudescence of symptoms,” he said.

Salix has already received FDA approval for Xifaxan to treat traveler’s diarrhea and hepatic encephalopathy, a brain disorder associated with severe liver disease. Salix has been trying to add IBS as a new indication for the drug to address an large unmet medical need. Only one drug, Prometheus Laboratories‘ Lotronex, has FDA approval to treat IBS with diarrhea. That drug has a black box warning.

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