• Proportion of subjects with undetectable plasma HIV-1 RNA (<50 copies/mL) [ Time Frame: 48 weeks ] [ Designated as safety issue: No ]
  

• Mean change from baseline in plasma HIV-1 RNA (log10 copies/mL); Proportion of subjects with <400 copies/mL of plasma HIV-1 RNA; Proportion of subjects with at least 2log10 reduction from baseline in plasma HIV-1 RNA [ Time Frame: 48 weeks ] [ Designated as safety issue: No ]
  

This is a randomized, double-blind, placebo-controlled, parallel-group, multi-center study of vicriviroc maleate in HIV subjects infected with CCR5-tropic virus only and who have documented resistance to at least 2 of the 3 antiretroviral drug classes (NRTI, NNRTI or PI) or at least 6 months experience with at least 2 of the following: one NRTI, one NNRTI, or two PIs (excluding low-dose ritonavir)and failed at least one standard triple-drug regimen. The study will compare the virologic benefit of adding vicriviroc to an optimized background regimen to a control group receiving placebo plus the new optimized background therapy. The optimized background regimen will be chosen by the investigator based on results of drug susceptibility tests performed at Screening, history of prior antiretroviral drug use by the patient, and drug toxicity. OBT must include a PI boosted by ritonavir, and at least 2 active drugs (ie, to which HIV isolate is fully susceptible). Primary efficacy analysis will be conducted when all subjects have completed 48 weeks of treatment. An interim analysis will be performed when all subjects have completed 24 weeks of treatment. If vicriviroc at the dose studied proves to be safe and efficacious, study participants who successfully complete 48 weeks of treatment or for whom vicriviroc is medically appropriate will be offered vicriviroc free of charge until the drug is commercially available.