Circadian variation of the urinary 6β-hydroxycortisol to cortisol ratio that would reflect hepatic CYP3A activity

Objectives: Chronopharmacokinetics of drugs metabolized by cytochrome P450 3A (CYP3A) has been reported recently; however, little is studied on intra-individual circadian variation in CYP3A activity in human. The aim of this study was to assess the intra-individual diurnal variation and day-to-day variation of the urinary 6β-hydroxycortisol to cortisol ratio, a noninvasive index of human CYP3A activity.