Dose-effect relationship of idebenone in an experimental cerebral deficit model. Pilot study in healthy young volunteers with piracetam as reference drug.

Within a general cerebral deficit model--inspiratory hypoxia-the dose--effect relationship of idebenone (CAS 58186-27-9), an antioxidant, was studied with regard to selected electrophysiological and psychometric parameters. Seventeen healthy male volunteers (mean age = 32 years, mean BW = 75 kg) received three different oral medications: placebo, idebenone and piracetam (CAS 7491-74-9) as reference. The test drug idebenone was administered in five different dosages, ranging--in 60 mg steps--from 60 to 300 mg t.id. Piracetam was given at a dose level of 800 mg t.i.d. A strict dose-regimen was used in idebenone for safety reasons. Each dosage/medication--except idebenone 300 mg t.i.d.--was given for one week without washouts in between. On each 7th treatment day, pharmacodynamic assessments comprising electroretinography (ERG), auditory evoked potentials (AEP) and visual analogue scales (VAS) were run. Immediately after the phases with the lower dosages, the study was continued with the highest dosage of idebenone (300 mg t.i.d.) for a period of four weeks with pharmacodynamic assessments on the 7th, 14th and 28th day. In this pilot study, the target variable, the amplitude of the ERG b-wave indicated a definite antihypoxidotic effect after the highest dosage of idebenone. With 300 mg idebenone t.i.d., ERG b-wave amplitudes increased linearily with increasing duration of treatment. The 'central' AEP P2-amplitude demonstrated a different dose-effect relationship. AEP P2-amplitudes increased with increasing dosages of idebenone. The prolongation of treatment with 300 mg t.i.d. resulted in no further improvement of this parameter (ceiling effect). Subjective ratings (VAS) by the volunteers confirmed the results seen in electrophysiological variables. The findings, however, remain to be confirmed within an adequate double-blind, crossover study design.