The Merit study was a randomized, double-blind, active-comparator multicenter, phase IIb/III study, treatment- naive patients (aged at least 16 years) with R5 HIV-1, and with plasma viral load (HIV-1 RNA) above 2000 copies/ml, who received MVC 300mg q.d., MVC 300mg b.i.d., or EFV 600mg q.d., each in combination with ZDV/3TC 300 mg/150mg b.i.d. Key exclusion criteria included prior treatment with EFV, ZDV, 3TC, or any antiretroviral for more than 14 days at any time, and evidence of resistance to EFV, ZDV, or 3TC, as indicated by the presence of at least one nucleoside-associated mutations conferring resistance to ZDV, or phenotypic resistance to ZDV, at least one mutation conferring resistance to 3TC or phenotypic resistance to 3TC, or at least one mutation responsible for EFV resistance or phenotypic resistance to EFV.