By Nathalie Tadena and Kristin Jones 
 

Idenix Pharmaceuticals Inc. (IDIX) said it will discontinue its clinical development program for two of its investigational treatments for hepatitis C, after the U.S. Food and Drug Administration said the treatments would remain on clinical hold.

Shares, which were halted briefly on the news, fell 9.7% to $4.27 after hours Monday. Through the close, the stock was down 42% in the past six months.

The treatments--IDX184 and IDX19368--were placed on clinical hold by the FDA in August. The clinical hold was related to the regulator's heart-safety concerns about rival Bristol-Myers Squibb Co.'s (BMY) treatment for the liver disease, BMS-986094, which belongs to the same class of drugs--known as nucleotide polymerase inhibitors.

In December, Idenix submitted cardiac safety data for IDX184 to the FDA, and the company said it "has found no evidence of severe cardiac findings to date." But the FDA told the company earlier this month that both treatments would remain on clinical hold.

Chief Executive Ron Renaud said the company intends to "maintain our strong presence in developing nucleotide polymerase inhibitors" for hepatitis C. It plans to file an investigational new-drug application for a separate compound in the first half of 2013 and to continue its preclinical developments of other nucleotide drugs.

Hepatitis C is a blood-borne virus that afflicts an estimated 4 million Americans and 170 million people world-wide. The disease often is contracted during sex or by sharing needles.

Current treatment of the drug requires long courses of painful injections and often doesn't work. Drug makers have been racing to find pills that are both more potent and easier to take.

Write to Nathalie Tadena at nathalie.tadena@dowjones.com and Kristin Jones at kristin.jones@dowjones.com

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