FDA places hold on AIDS drug

The US Food and Drug Administration (FDA) has placed a clinical hold on an experimental HIV/AIDS drug being developed by GlaxoSmithKline (GSK) under a licence from Idenix Pharmaceuticals.

The drug, GSK2248761, is a novel HIV non-nucleoside reverse transcriptase inhibitor (NNRTI) that was licensed to GSK by Idenix in 2009 in a deal that could be worth more than $450m. The once-daily, lower-dose NNRTI is intended to offer an improved drug resistance and pharmacokinetic profile and was performing well in phase II clinical trials at the time the deal was signed.

In revealing the clinical hold, Idenix did not give any reason for the FDA's action. The company said it was informed of the hold by ViiV Healthcare, an affiliate of GSK.

Idenix has so far received $60.5m in licence fees under the deal and is eligible to receive up to $390m in milestone payments, as well as royalties on sales.

Idenix out-licensed the HIV drug in order to focus on its hepatitis C drug candidates. Along with announcing the clinical hold on GSK2248761, the company also provided updates on two potential therapies for hepatitis C virus (HCV).

The company said that the FDA has lifted a full clinical hold on IDX184, a liver-targeted HCV nucleotide prodrug. The full clinical hold, under which no new or existing patients could be administered the drug, was issued in September 2010 after three cases of elevated liver function tests were observed in subjects during a drug-drug interaction study of the combination of IDX184 and IDX320, an HCV protease inhibitor, in healthy volunteers.

After reviewing the data and conducting additional preclinical studies, Idenix determined that the toxicity was likely caused by IDX320 and so has discontinued development of that drug. A partial clinical hold remains on IDX184. However, Idenix said it expects to begin a phase IIb12-week trial of IDX184 in combination with pegylated interferon and ribavirin in the second half of this year.