Four phase 1 studies were conducted to assess the pharmacokinetics and metabolism of idebenone (including parent drug and inactive metabolites QS10, QS6, and QS4) and to evaluate the safety of a wide range of idebenone doses and regimens in healthy adult men. After a single oral dose of idebenone 150 mg, 750 mg, or 1050 mg in fasted or fed subjects, blood samples were taken for up to 72 hours. In one study, after a single oral dose and a 7-day washout period, subjects received repeated doses of idebenone 150 mg or 750 mg every 8 hours for 14 days. In the repeated-dose study, urine samples also were taken. Plasma and urine samples were analysed with the use of liquid chromatography with tandem mass spectrometry. Non-compartmental standard pharmacokinetic methods were used. In these studies, a total of 69 subjects ranging in age from 19 to 41 years (body weight, 57-94.6 kg) were included. Plasma concentrations of parent idebenone were low but increased in proportion to dose and increased approximately five-fold in the presence of food. Total QS4 was the main metabolite in plasma and urine. The most common adverse events were loose stool, fatigue, headache, and disturbances in attention. Idebenone was well tolerated in single oral doses up to 1050 mg and in repeated daily doses up to 2250 mg. Idebenone showed linear pharmacokinetics after single and repeated oral dosing. Administration after a meal resulted in the highest exposure to parent idebenone.