Randomized, Double-Blind Study Comparing Dexelvucitabine (DFC) to Lamivudine (3TC) in Subjects With Resistance to NRTIs, PIs, and NNRTIs

The study will compare the safety and efficacy of an investigational nucleoside analog reverse transcriptase inhibitor (NRTI), dexelvucitabine (DFC) 200 mg once daily, to an approved NRTI, lamivudine (3TC) 300 mg once daily in treatment experienced patients with HIV that is resistant to 3 classes of antiretroviral therapies (NRTIs, PIs and NNRTIs). Patients meeting eligibility requirements will have a new 'optimized' background regimen (OBR) selected for them based on prior treatment history, and results of HIV genotype and phenotype performed during screening. In addition to the OBR patients will be randomized to receive at at one to one ratio DFC or 3TC in a blinded fashion. The OBR may include any approved HIV treatments except 3TC, FTC, ddI, d4T and ddC. Medications available through expanded access may also be available to selected patients. Treatment in the study will continue for up to 96 weeks with primary endpoints at 24 and 48 weeks of therapy. Patients with an inadequate response to therapy after 16 weeks will have the option to change their OBR and the option to switch study medication (DFC to 3TC or 3TC to DFC). A total of 250 patients will be enrolled.