Objective:A severe dose-limiting axonal peripheral neuropathy may develop in subjects on treatment with the nucleoside analogues didanosine (ddI), zalcitabine (ddC), and stavudine (d4T). The impairment of mitrochondrial DNA synthesis is crucial to the pathogenesis of this disorder although other mechanisms have not been ruled out. The depletion of acetyl-carnitine, which regulates the metabolism and function of peripheral nerves, could contribute to the neurotoxicity of these compounds.Design:Non-randomized, cross-sectional study of selected patients.Methods:We measured the serum levels of acetyl- and total carnitine in 12 subjects with axonal peripheral neuropathy developed on treatment with different regimens of neurotoxic nucleoside analogues (ddI, ddC, d4T). Subjects who did not develop peripheral neuropathy while staying on treatment with ddI (n = 10) or zidovudine (n = 11) served as the control groups. HIV-negative subjects with axonal or demyelinating autoimmune neuropathies (n = 10) and healthy individuals (n = 13) were additional control groups.Results:Subjects experiencing axonal peripheral neuropathy on treatment with ddI, ddC and d4T had significantly reduced levels of acetyl-carnitine in comparison to the control groups. No difference was observed in the levels of total carnitine between study subjects and the control groups.Conclusions:Our results demonstrate that subjects who developed peripheral neuropathy while staying on treatment with ddI, ddC and d4T had acetyl-carnitine deficiency. The normal levels of total carnitine in the study group appear to indicate the specificity of the defect and rule out coexisting relevant nutritional problems. The critical role of acetyl-carnitine for the metabolism and function of the peripheral nerves supports the view that the acetyl-carnitine deficiency found in these subjects may contribute to the neurotoxicity of ddI, ddC and d4T, even though the interference with mitochondrial DNA synthesis is regarded as the main cause of their toxicity.