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Background: The use of either efavirenz or lopinavir-ritonavir plus two nucleoside reverse-transcriptase inhibitors (NRTIs) is recommended for initial therapy for patients with human immunodeficiency virus type 1 (HIV-1) infection, but which of the two regimens has greater efficacy is not known. The alternative regimen of lopinavir-ritonavir plus efavirenz may prevent toxic effects associated with NRTIs., Methods: In an open-label study, we compared three regimens for initial therapy: efavirenz plus two NRTIs (efavirenz group), lopinavir-ritonavir plus two NRTIs (lopinavir-ritonavir group), and lopinavir-ritonavir plus efavirenz (NRTI-sparing group). We randomly assigned 757 patients with a median CD4 count of 191 cells per cubic millimeter and a median HIV-1 RNA level of 4.8 log10 copies per milliliter to the three groups., Results: At a median follow-up of 112 weeks, the time to virologic failure was longer in the efavirenz group than in the lopinavir-ritonavir group (P=0.006) but was not significantly different in the NRTI-sparing group from the time in either of the other two groups. At week 96, the proportion of patients with fewer than 50 copies of plasma HIV-1 RNA per milliliter was 89% in the efavirenz group, 77% in the lopinavir-ritonavir group, and 83% in the NRTI-sparing group (P=0.003 for the comparison between the efavirenz group and the lopinavir-ritonavir group). The groups did not differ significantly in the time to discontinuation because of toxic effects. At virologic failure, antiretroviral resistance mutations were more frequent in the NRTI-sparing group than in the other two groups., Conclusions: Virologic failure was less likely in the efavirenz group than in the lopinavir-ritonavir group. The virologic efficacy of the NRTI-sparing regimen was similar to that of the efavirenz regimen but was more likely to be associated with drug resistance. (ClinicalTrials.gov number, NCT00050895 [ClinicalTrials.gov].)., (Copyright 2008 Massachusetts Medical Society.)