These data come from ACTG 368 which is a roll-over trial of ACTG 320, in an effort to learn optimal therapeutic strategies for patients already experienced with nucleoside analogues (NRTI) but who are no longer receiving any benefit from them. In this study, 283 individuals who were naïve to both PI and NNRTIs but who had received at least two months of combination NRTI therapy (AZT or D4T with 3TC) were then randomized to receive either abacavir (ABV) or placebo. Further randomization occurred for patients with CD4>50 within each ABV group so that they received Efavirenz with indinavir in one of two dose schedules (twice daily or thrice daily indinavir), and was designed to make two comparisons: ABV with placebo, and twice daily versus thrice daily indinavir.

In evaluating the two indinavir dose schedules at 16 weeks, there was no significant difference between twice daily (BID) and thrice daily (TID) dosing in terms of achieving levels of viral suppresson below 500 copies: 83% went below 500 in the TID group, and 74% in the BID group (p=0.16). However, by 32 weeks, a significant difference emerged (p=0.025) as 81% remained undetectable in the TID group as opposed to 62% in the BID arm. Furthermore, this difference persisted at 48 weeks, and as a result Merck terminated all studies comparing TID with BID dosing. No differences in CD4 counts were seen between groups.

The ABV versus placebo comparison is still ongoing, but at 48 weeks, there is no difference in either arm in the achievement of viral load levels below 500.