Virologic Responses To New Nucleoside Regimens After Prolonged ZDV or ddI Monotherapy

To elucidate the relationship between virologic risk factors and immunologic and clinical progression in patients receiving monotherapy in protocol ACTG 175, and to compare new treatment regimens with combinations of reverse transcriptase inhibitors in long-term recipients of monotherapy. Specifically, to determine, in patients who have been taking zidovudine (AZT) alone for a long time, whether it is beneficial to add lamivudine (3TC) to AZT or to switch to d4T alone, and also to determine, in patients who have been taking didanosine (ddI) alone for a long time, whether it is beneficial to add AZT or AZT/3TC to ddI. Characteristics of virus replication, pathogenicity, and resistance are thought to determine the durability of virologic and clinical response to nucleoside reverse transcriptase inhibitors. Previous results of ACTG 175 suggest that either a switch to ddI or addition of ddI in patients receiving AZT results in better clinical, virologic, and CD4 cell response compared to continuation of AZT alone.