Patent ID: 6905839

Claim:
A method for evaluating the level of in vivo CYP3A activity to metabolize CYP3A substrate substances of a subject by measuring metabolic clearance for the 6β-hydroxylation of cortisol in said subject as an index for said in vivo CYP3A activity without use of labeled exogenous cortisol, wherein the method comprises the steps of: (a) collecting urine sample of said subject accumulated in a urine collection period and obtaining a blood sample of said subject at least once during said urine collection period; (b) measuring the cortisol concentration in plasma or serum of said blood sample or samples and calculating the area under the plasma or serum concentration-time curve of cortisol (AUC (F) ) of said urine collection period; (c) measuring the volume and the 6β-hydroxycortisol concentration of said urine sample to determine the total amount (X(6β)) of 6β-hydroxycortisol excreted in the urine during said urine collection period; (d) calculating the metabolic clearance (CLm(6β)=X(6β)/AUC (F) ) for the 6β-hydroxylation of cortisol as an index of in vivo CYP3activity of said subject at the time when said measurements are made.