Schering-Plough Corporation announced today that it has begun enrolling a phase II study of its experimental CCR5-blocking entry inhibitor vicriviroc for people starting HIV treatment for the first time. Unlike standard drug combinations used to treat HIV-positive people new to antiretroviral (ARV) treatment, the vicriviroc regimen being tested in this study does not use any nucleoside reverse transcriptase inhibitors (NRTIs), reserving them for use in subsequent drug combinations and potentially reducing the risk of certain side effects. 

In the study, to be conducted in North America, Central America, Europe and South Africa, 200 patients will be allotted to receive either 30 mg vicriviroc once daily combined with Norvir (ritonavir)-boosted Reyataz (atazanavir) or the fixed-dose NRTI pair Truvada (tenofovir plus emtricitabine) plus Norvir-boosted Reyataz.

Another phase II study of vicriviroc, which is similar to Pfizer’s approved drug Selzentry (maraviroc), in heavily treatment-experienced people found it to be superior to placebo in terms of viral load reductions and CD4 gains. In that trial, called VICTOR-01, vicriviroc was taken along with an optimized background regimen (OBR) of other ARVs and was compared with a placebo plus OBR. Patients in the vicriviroc arm did not have a greater rate of side effects than those in the placebo arm.