Idenix Pharmaceuticals receives clinical hold order from FDA for IDX184, IDX320 programs

Idenix Pharmaceuticals, Inc. (Nasdaq: IDIX), a biopharmaceutical company engaged in the discovery and development of drugs for the treatment of human viral diseases, today announced that the company received verbal notice on Friday, September 3, 2010 from the U.S. Food and Drug Administration (FDA) that the IDX184 and IDX320 programs have been placed on clinical hold.  A clinical hold is an order issued by the FDA to the sponsor to delay a proposed clinical investigation or to suspend an ongoing investigation. This decision was made after Idenix notified the FDA of three serious adverse events that occurred during a drug-drug interaction study of the combination of IDX184 and IDX320 in healthy volunteers. These observed serious adverse events were elevated liver function tests detected in three subjects during post exposure safety visits. The liver function tests have returned to nearly normal levels in all three subjects during follow-up. All planned studies of IDX184 and IDX320 to date have been completed and there are currently no healthy volunteers or patients receiving IDX184 or IDX320. Idenix will submit full data to the FDA from recently completed preclinical and clinical studies, including 3-month chronic toxicology studies of IDX184, a 14-day study of IDX184 in combination with pegylated interferon/ribavirin (PegIFN/RBV), a 3-day proof-of-concept study of IDX320 in hepatitis C (HCV) infected patients, and the IDX184 and IDX320 drug-drug interaction study in healthy volunteers in order to assess next steps in the development of both compounds.

"We have not yet received a formal letter from the FDA, nor has the Agency had an opportunity to review the safety and efficacy data from recently completed clinical trials with IDX184 and IDX320. Based upon our discussions with the Agency, we are primarily focused on three cases of elevated liver function tests observed during our drug-drug interaction study of the combination of IDX184 and IDX320 in healthy volunteers," said Jean-Pierre Sommadossi, Ph.D., Idenix Chairman and Chief Executive Officer. "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. 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."

Full data presentations of IDX184, IDX320 and IDX375 studies will be presented at the annual meeting of the American Association for the Study of Liver Diseases (AASLD), which will be held at the end of October in Boston.

Phase I: IDX184/IDX320 Combination

Idenix completed a two-week Phase I, randomized, double-blind, placebo-controlled study to evaluate the safety and pharmacokinetic drug-drug interaction between IDX320 and IDX184 in healthy volunteers. Two cohorts were evaluated in the study with 10 subjects in each cohort randomized eight to active drug and two to placebo. Subjects in the first cohort received 400 mg once-daily of IDX320 for the first week, subsequently adding 100 mg once-daily of IDX184 for the second week. Subjects in the second cohort received 100 mg once-daily of IDX184 plus placebo for the first week, subsequently adding 400 mg once-daily of IDX320 for the second week. The combination of IDX184 and IDX320 was generally safe and well tolerated during the 14 days of treatment. Liver function abnormalities deemed to be serious adverse events were detected in three subjects during the post exposure safety visits. Liver function tests in these subjects have returned to nearly normal during follow-up.  Pharmacokinetic drug-drug interactions between IDX184 and IDX320 were not considered to be clinically significant. Neither the plasma exposure of IDX184 and its metabolite, 2'-methylguanosine, nor IDX320 plasma exposure explain these three serious adverse events.

Phase IIa: IDX184, a liver-targeted HCV nucleotide prodrug

This 14-day, Phase IIa clinical trial evaluated 50 to 200 mg doses of IDX184 in combination with PegIFN/RBV in treatment-naive HCV genotype 1-infected patients. At Day 14, mean (+/- standard deviation) viral load reductions were  1.5 (+/- 1.3) logs for placebo>

Phase I/II: IDX 320, an HCV protease inhibitor

This randomized, parallel-arm, double-blind, placebo-controlled proof-of-concept trial evaluated the safety, tolerability, antiviral activity and pharmacokinetics of IDX320 in treatment-naive HCV genotype 1-infected patients. Thirty patients were randomized equally and received placebo, 50, 100, 200 or 400 mg of IDX320 orally once-a-day for three days. One cohort of eight patients was randomized to receive 200 mg IDX320 BID or placebo. At Day 3, mean (+/- standard deviation) viral load reductions were 0.1 (+/- 0.15) logs for  placebo>

Phase I: IDX375, an HCV non-nucleoside polymerase inhibitor

Idenix has an ongoing Phase I clinical trial in healthy volunteers evaluating single doses of the free acid form of IDX375 ranging from 200 to 1200 mg per day.  Overall, IDX375 achieved pharmacologically relevant drug exposure and was well tolerated for doses up to 1200 mg for one day in healthy subjects. In the fourth quarter of 2010, Idenix plans to initiate a 3-day proof-of-concept trial in treatment-naive genotype 1 HCV-infected patients.

SOURCE Idenix Pharmaceuticals, Inc.