FDA places partial clinical hold on Idenix's hepatitis C drug IDX184

Idenix Pharmaceuticals reported Thursday that the FDA placed a partial clinical hold on IDX184 and has requested further safety data on the experimental hepatitis C drug. Shares in the company fell as much as 35 percent on the news.

According to Idenix, the agency verbally informed the drugmaker of the decision which was taken after "the recent occurrence of a serious cardiac-related adverse event encountered with" Bristol-Myers Squibb's similar nucleotide polymerase inhibitor BMS-986094. Idenix noted that in an ongoing Phase IIb study of IDX184 in combination with pegylated interferon and ribavirin, as well as in earlier trials, "there has been no evidence to date of cardiotoxicity in patients" given the investigational agent.

In February, the FDA lifted a partial clinical hold on IDX184 issued in 2010 after three cases of elevated liver function tests were observed in the Phase IIb study. The company said Thursday that it is trying to track down 67 patients who took the drug so they can perform cardiac tests on them and expects to submit the required information to the regulator in the coming weeks. Chief scientific officer Douglas Mayers noted that all of the patients have been off the medicine for at least a month.

Idenix CEO Ron Renaud indicated that the FDA is looking at other compounds from the same class of medicines as IDX184. "They did mention they'd be looking at, to start, NS5B polymerase inhibitors," Renaud said, adding that he didn’t know whether the agency would look at all of the related drugs that are in clinical development or just some.

Commenting on the news, Sanford C. Bernstein & Co. analyst Geoffrey Porges said "this event is likely to raise concerns about the risks of nuke programmes across the spectrum, but we believe it is important to understand the difference among the assets." Porges added that similar compounds from Gilead Sciences and Vertex Pharmaceuticals have different structures and may not raise the same worries.

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