Switch From Combivir or Trizivir to Truvada - Mitochondrial Effects

Study subjects receiving the antiretroviral drugs Combivir or trizivir, will be randomized to switch to Truvada-containing highly active antiretroviral therapy (HAART) or to continue on Combivir or on trizivir. Measurements will be performed at baseline and after 6 months after randomization to either continuing on trizivir or combivir, or to switching to Truvada. Measurements include maximal or peak oxygen consumption, lactate production and clearance, subcutaneous adipose tissue and limb fat contents, insulin resistance, liver and muscle fat contents, and plasma free fatty acid concentrations. The hypothesis underlying this study is that chronic therapy with thymidine analogue nucleoside reverse transcriptase inhibitors (NRTIs), including zidovudine (AZT), leads to clinically detectable mitochondrial dysfunction in several organ systems.