UPDATED: Idenix craters as clinical hold spurs tox jitters for hot hep C drug

Idenix Pharmaceuticals ($IDIX) went into free fall this morning, tumbling about 40% on the news that its nucleotide polymerase inhibitor IDX184 was put on partial clinical hold as the FDA studies whether a recent cardiac event that may well have spiked a similar treatment at Bristol-Myers Squibb ($BMY) raises similar toxicity issues for Idenix.

"In previous clinical trials as well as the ongoing Phase IIb clinical trial of IDX184 in combination with pegylated interferon and ribavirin (PegIFN/RBV), there has been no evidence to date of cardiotoxicity in patients dosed with IDX184 with PegIFN/RBV beyond that seen with PegIFN/RBV alone," Idenix cautioned this morning in a short statement. But even a whiff of this kind of trouble is enough to spook investors who have bid up shares in hopes of cashing in on new treatments.

Cambridge, MA-based Idenix has been among the leaders in the mad scramble to advance new "nucs" and NS5A inhibitors that can be combined with ribavirin into an all-oral regimen with megamarket potential. But the quest for the new holy grail in biotech has been slowed by a cardiac event that has halted work on BMS-094. Analysts have pointed to a somewhat similar chemical structure between BMS-094--formerly INX-189 before Bristol bought Inhibitex in a $2.5 billion deal--and IDX184, which has sent shivers down investors' spines.

Bernstein's Geoffrey Porges, though, think the differences outweigh the similarities of the two therapies. "This event is likely to raise concerns about the risks of nuke programs across the spectrum, but we believe it is important to understand the difference among the assets," he notes, according to Bloomberg.

Bristol-Myers hasn't written off its once-hot hep C drug, but it is pondering the move. Cardiovascular side effects have triggered the demise of many therapies and regulators have no tolerance for subjecting patients to potential risks in the clinic. Novartis ($NVS) recently relinquished its hep C partnership with Idenix, though most analysts have seen that as a positive move for the developer--at least until now.

- here's the press release
- here's the Bloomberg report

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