Dmd048561 475..479

This study was designed to evaluate the in vivo activity of cytochrome P450 3A (CYP3A) in 49 healthy Japanese subjects aged 22–58 years using endogenous cortisol 6b-hydroxylation clearance [CLm(6b)], a novel biomarker for CYP3A phenotyping. CLm(6b) in the 49 healthy subjects was 2.40 6 0.79 ml/min with an approximately 4fold interindividual variability of CYP3A activity. The mean clearance in the 24 women was 2.50 6 0.89 ml/min; the value in the women was higher than in the 25 men (2.30 6 0.69 ml/min) by approximately 9%. We also measured the change of CLm(6b) in 14 healthy subjects in the morning at 10:00–12:00 every 2 or 3 days over a period of 36–53 days and observed a 1.5-fold to 3.4-fold dayto-day intraindividual variability in the CYP3A activity. The mean value for CLm(6b) in each subject for 36–53 days was 2.54 6 0.76 ml/min (n = 14). We also evaluated the CLm(6b) every 2 hours from 8:00–20:00 in 26 healthy subjects. The within-day intraindividual clearance variability was 1.1-fold to 2.5-fold (2.45 6 0.91 ml/min, n = 26). No characteristic diurnal rhythms were observed in the in vivo