In virologically stable treatment-experienced adults, emtricitabine, in combination with an NRTI (either stavudine or zidovudine) and a protease inhibitor (PI) or an NNRTI was shown to be non-inferior to lamivudine with respect to the proportion of responders (< 400 copies/ ml) through 48 weeks (77% emtricitabine, 82% lamivudine).