Correlation between reduction in plasma HIV-1 RNA concentration 1 week after start of antiretroviral treatment and longer-term efficacy

Background Early assessment of antiretroviral drug efficacy is important for prevention of the emergence of drug-resistant virus and unnecessary exposure to ineffective drug regimens. Current US guidelines for changing therapy are based on measurements of plasma HIV-1 RNA concentrations 4 or 8 weeks after the start of treatment with cut-off points of 0·75 or 1·00 log, respectively. We investigated the possibility of assessing drug efficacy from measurements of plasma HIV-1 concentrations made during the first week on therapy. Methods The kinetics of virus decay in plasma during the first 12 weeks of treatment was analysed for 124 HIV-1-infected patients being treated for the first time with a protease inhibitor. Patients with a continuous decline of HIV-1 concentrations and in whom HIV-1 was either undetectable or declined by more than 1·5 log at 12 weeks were defined as good responders; the rest were poor responders. Findings The individual virus decay rate constants (k) at day 6 correlated significantly (r>0·66, p<0·0001) with changes in HIV-1 concentrations at 4, 8, and 12 weeks, and correctly predicted 84% of the responses with a cut-off value of k=0·21 per day (in log scale). Reduction in plasma HIV-1 of less than 0·72 log by day 6 after initiation of therapy predicted poor long-term responses in more than 99% of patients. Interpretation These results suggest that changes in HIV-1 concentration at day 6 after treatment initiation are major correlates of longer-term virological responses. They offer a very early measure of individual long-term responses, suggesting that treatment could be optimised after only a few days of therapy.