Merck will not seek vicriviroc licenses in treatment-experienced

Keith Alcorn
Published: 21 January 2010

Merck has announced that it will not press ahead with attempts to obtain a license for vicriviroc in treatment-experienced patients with HIV following disappointing results in two phase III studies that were designed to clinch approval of the drug.

Vicriviroc, a CCR5 inhibitor, was acquired as part of Merck’s merger with Schering-Plough. The drug is designed to block the CCR5 receptor that HIV uses to infect cells.

The CCR5 inhibitor class of antiretroviral drug has been beset by development problems and a commercial disappointment.

The first product in this class of antiretroviral drug, maraviroc, has been approved for use in both treatment-experienced and treatment-naive patients, but an earlier analysis of a phase III study, using a less sensitive test for virus that exploits the CCR5 receptor, suggested the drug was inferior to efavirenz. Subsequent analysis using a more sensitive test showed that the two drugs had broadly equivalent antiviral effects.

Glaxo SmithKline abandoned development of another CCR5 inhibitor, aplaviroc, in 2005 after cases of severe liver toxicity in a phase II study of the drug.

And a study of vicriviroc itself, in treatment-naive patients, was terminated after cases of early viral load rebound in some vicriviroc recipients.

The trials that led to Merck's decision were two phase III studies that recruited treatment-experienced patients. Participants in the VICTOR E3 and E4 studies received an optimised background regimen determined by resistance testing to maximise the number of active drugs they received, and were randomised to receive vicriviroc or a placebo.

An announcement on the company’s website stated that "In two Phase III studies in this patient population, vicriviroc did not meet the primary efficacy endpoint.”

According to Reuters the trials enrolled a high proportion of patients with three or more active drugs in the optimised background regimen.

Merck says it will not be proceeding with a filing for a US product license in treatment-experienced patients, but will be continuing studies of the drug in treatment-naïve patients.

Vicriviroc is being tested in treatment-naïve patients as part of an innovative nucleoside-sparing regimen, in combination with atazanavir/ritonavir.

More information on the cancellation of development plans in treatment-experienced patients is expected to be available on January 22nd, when Merck will brief treatment advocates. Full results of the studies are expected to be presented next month at the Conference on Retroviruses and Opportunistic Infections.

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