Unfortunate news was recently released by Merck on their experimental co-receptor antagonist, vicriviroc, which might have provided another option as the second R5 drug, just behind Selzentry (maraviroc). The company will not move forward for FDA approval given the disappointing results from 2 large studies (VICTOR-E3 and -E4) in treatment-experienced people. Complete data will be released at CROI (Conference on Retroviruses and Opportunistic Infections) in February 2010.
Both studies followed people who had been on therapy before. Everyone was on effective HIV therapy (3 or more active drugs) and was then randomly assigned to take vicriviroc or placebo. A press release by the company stated that the studies did not meet their main goal, most likely not keeping HIV under control and below 50 copies over time. Vicriviroc is still being studied in those starting their first HIV regimen.