[Circadian rhythms in hepatic biotransformation of drugs].

The temporal variations in hepatic drug biotransformation are reviewed. Important diurnal variations in the activity of different cytochrome P-450 isoenzymes and in enzyme systems involved in conjugation to glucuronide, sulfate and acetate are described. A circadian rhythm in the hepatic concentration of glutathione is also described. These temporal variations explain the chronopharmacokinetic and chronohepatotoxicity of some drugs or toxic agents.