Idenix: Two Hep C Drugs on Clinical Hold

CAMBRIDGE, Mass. (TheStreet) -- Idenix Pharmaceuticals(IDIX) was forced to suspend clinical development of its two most advanced hepatitis C drug candidates after possible liver toxicity was discovered in healthy volunteers exposed to the drugs.

The U.S. Food and Drug Administration informed Idenix on Friday that it was placing IDX184 and IDX320 on clinical hold, pending further data to be submitted to the agency, Idenix announced Monday.

Idenix shares are down 55% to $2.70 in Monday's pre-market session. The stock had been one of the leading performers in the biotech sector so far this year.

The clinical hold comes at a particularly bad time for Idenix because the company has been seeking development partners for its most advanced hepatitis C drug candidates.

No clinical trials involving either IDX184 or IDX320 are ongoing, the company added.

Idenix says three healthy volunteers dosed with both IDX184 and IDX320 in a drug-drug combination study were found to have elevated liver enzymes in a routine post-study safety monitoring examination. Subsequently, liver function tests for all three patients returned to normal. Idenix said it notified the FDA of the liver function problems, at which point the agency asked that the two drugs be placed on clinical hold.

"Based upon the safety and antiviral activity we observed in the IDX184 14-day study and the IDX320 3-day proof-of-concept study, both in HCV-infected patients, we remain committed to the future potential of these drug candidates," said Idenix CEO Jean-Pierre Sommadossi. "We will work closely with independent experts and our external safety committee to better understand the cause of these serious adverse events in the combination study of IDX184 and IDX320 and to provide the FDA with more information in order to expedite their review and resolve this matter as quickly as possible."

Liver toxicity has not yet cropped up as a concern when either IDX184 or IDX320 was studied on its own. IDX184 is Idenix's most advanced hepatitis C drug candidates, having completed a 14-day study where IDX184 was tested in combination with pegylated interferon and ribavirin, the current standard of care for hepatitis C.

IDX320 is still in early-stage studies on its own in hepatitis C, although Idenix has also started testing a combination of IDX184 and IDX320.

Data from studies of both drugs are expected to be presented at the American Association for the Study of Liver Diseases (AASLD) annual meeting, which will be held at the end of October in Boston. Other companies presented data at the meeting include Vertex Pharmaceuticals(VRTX), Merck(MRK), Bristol-Myers Squibb(BMY), InterMune(ITMN) and Pharmasset(VRUS), among others.