 The results from a 48-week phase II trial (VICTOR-E1) examining administration of 20 or 30 mg dosages of vicriviroc in addition to > 3-drug optimized background therapy (OBT) regimen that included a ritonavir-boosted protease inhibitor were reported in February 2008.Investigators concluded that, “‘Vicriviroc 30 or 20 mg once daily plus ritonavir-containing OBT provided sustained viral suppression in treatment-experienced subjects and increased CD4 cell counts regardless of the number of active drugs in OBT.’"

As of May 2008, two phase III trials (VICTOR-E3 and VICTOR E4) in treatment-experienced patients were initiated.The late stage clinical trials by did not meet their primary efficacy endpoints and Merck has decided as of January 2010 to not pursue regulatory approval for the drug.