In vitro activity: Stavudine alteres the lipid phenotype, decreasing the lipid content and expression of markers involved in lipid metabolism, namely C/EBPalpha, peroxisome proliferator-activated receptor gamma, adipocyte lipid binding protein 2, fatty acid synthase and acetyl-coenzyme A carboxylase. Stavudine drives 5-10% of 3T3-F442A cells towards apoptosis, and reduces the lipid content and survival of differentiated 3T3-L1 adipocytes. Stavudine increases mitochondrial mass by two to fourfold, and loweres the mitochondrial membrane potential (JC-1 stain). Stavudine inhibits p24 antigen production by HIV-I in PBMC with EDsos ranging from 0.04 μM to 0.2 μM. Stavudine produces significant mitochondrial dysfunction with a 1.5-fold increase in cellular lactate to pyruvate ratios. Stavudine causes a dose-dependent decrease in mtDNA amplification and a correlative increase in abundance of markers of mitochondrial oxidative stress. Stavudine treatment elevates mitochondrial reactive oxygen species (ROS), enhances mitochondrial oxidative stress, and contributes mechanistically to NRTI-induced toxicity.