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Merck Reports Initial Results of Phase III Studies with Vicriviroc in Treatment-Experienced HIV-Infected Patients

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Merck has reported initial pooled results from two Phase III studies of vicriviroc, its investigational HIV CCR5 receptor antagonist, in treatment-experienced HIV-infected patients, and said that based on these results it will not submit a New Drug Application (NDA) for vicriviroc in this patient population at this time.

In the two Phase III studies, vicriviroc did not meet the primary efficacy endpoint of superiority over optimized background therapy (OBT). The company is evaluating alternative ways to move ahead with this investigational agent.

Data from the Phase III studies were presented at the 17th Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco.

Vicriviroc is an extracellular inhibitor of HIV infection, and is designed to prevent the virus from infecting the immune system’s CD4 cells by blocking its primary entry route, the CCR5 co-receptor. Approximately 50 to 60 percent of treatment-experienced patients and 80 to 90 percent of treatment-naïve patients have virus that uses the CCR5 co-receptor (R5-type virus).

The two Phase III studies in treatment-experienced HIV-infected patients, known as VICTOR-E3 and E4, compared vicriviroc (30 mg once daily) to placebo in combination with an OBT regimen in which at least two fully active antiretroviral drugs were required and which included a ritonavir-boosted protease inhibitor.

More than 60 percent of patients in these studies had three or more active drugs in their OBT regimen, which is a substantially greater proportion than in recent studies for other HIV therapies. In the vicriviroc studies, 64 and 62 percent of patients in the vicriviroc and placebo arms, respectively, had undetectable virus (HIV-1 RNA less than 50 copies/mL) at week 48 of treatment, the primary efficacy endpoint, and this difference did not reach statistical significance (p=0.6).

“While these results are disappointing, it is becoming increasingly difficult for an additional HIV medicine to demonstrate a significant incremental benefit as the fourth or fifth drug added to optimized background therapy," said Lisa Dunkle, M.D., executive director clinical research, Merck Research Laboratories. “We will further evaluate these results to better understand these findings and define a potential path forward for vicriviroc.”

The company said that an ongoing, fully enrolled Phase II clinical study of vicriviroc in treatment-naïve HIV-infected patients will continue unchanged, and this is supported by an external, independent Data Safety Monitoring Board. Treatment-experienced patients from the vicriviroc clinical trials who are benefiting from vicriviroc treatment will continue to have access to the medicine as provided for in the trial protocols.