Design: Our primary objective is to examine the tolerability of idebenone given at a dose of 60 mg/kg/day for 72 hours (total of 9 doses) in an inpatient setting (NIH Clinical Center). This dose is below the maximum dose examined (75 mg/kg/day) that was well tolerated with no dose-limiting toxicity (DLT) in our phase 1A (protocol# 01-N-0167) study. The 72 hour course represents 5.5 half-lives of the drug based upon previous studies of the drug in healthy human subjects and our phase 1A data, thereby allowing the serum concentration of the drug to reach steady-state levels. This multiple dose regimen will allow us to examine accumulation of the drug and to examine tolerability of the drug at a steady-state concentration. The patients will then be followed by inpatient monitoring for an additional 43 hours, representing 3.3 half-lives, to allow relatively complete elimination of the drug. If no adverse events are noted during the inpatient phase of the trial, patients will resume taking the drug on an outpatient basis for 1 month to determine long-term tolerability and compliance. Outpatients will be followed through phone interviews by the NIH research team along with routine blood work every 2 weeks. Our secondary objective is to document the pharmacokinetics, specifically the apparent distribution volume (Vd), elimination half-life (t1/2), elimination clearance (CLE), and steady-state concentrations (CSS) of idebenone during the inpatient phase of the study.