Patients are randomized to 1 of 2 arms in a 2:1 ratio. Approximately 260 patients receive ADV and approximately 130 patients receive placebo. Patients receive ADV or placebo in addition to L-carnitine and their current stable HAART regimen. Each patient receives blinded study medication for 48 weeks and is evaluated at Weeks 16, 24, and 48. Patients who reach the primary endpoint of virologic failure prior to Week 48 may continue blinded study medication or receive open-label ADV at the investigator's discretion. In both cases, patients continue their study visits as per the original visit schedule. Virologic failure is defined as 2 consecutive HIV-1 RNA measurements, after baseline, above 400 copies/ml (measured by the Roche Amplicor HIV-1 Monitor UltraSensitive assay) drawn at least 14 days apart. All patients who complete study visits without treatment-limiting ADV toxicity may continue open-label ADV in the Maintenance Phase at the discretion of the principal investigator.