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Interindividual and Intraindividual Variability of the Urinary 6ß-Hydroxycortisol/Cortisol Ratio in Chinese Subjects: Implications of Its Use for Evaluating CYP3A Activity

From the School of Pharmacy, Faculty of Medicine, the Chinese University of Hong Kong, Shatin, New Territories, Hong Kong (Dr Yin, Dr Chow); Department of Pharmacy, Huashan Hospital, Fudan University, Shanghai, China (X. Shi); and Department of Medicine and Therapeutics, Faculty of Medicine, the Chinese University of Hong Kong, Shatin, New Territories, Hong Kong (Dr Tomlinson).

The present study determined the interindividual and intrandividual variability of the urinary 6ß-hydroxycortisol/cortisol ratio, a useful marker for CYP3A induction and inhibition in Chinese subjects. The study consisted of 2 parts. In part I, 82 healthy male Chinese subjects underwent 3 study sessions, each separated by a 1-week interval. In part II, 20 subjects who initially completed part I underwent another 3 sessions over a period of 3 to 4 months. During each session, a first-morning urine specimen was collected from each subject for the quantification of urinary concentrations of cortisol and 6ß-hydroxycortisol. There were no significant differences in the mean 6ß-hydroxycortisol/cortisol ratios among the 3 sessions (P > .05, 1-way analysis of variance) for both part I and part II of the study. A normal distribution of the 6ß-hydroxycortisol/cortisol ratio was observed (P = .849, Kolmogorov-Smirnov test). This ratio varied 30-fold (range, 0.76-23.23) among the study subjects. The mean intraindividual variabilities during the short (3-week) and long (3- to 4-month) periods were 30.9% ± 17.5% and 32.2% ± 17.1%, respectively. The genetic fraction contributing to the observed variability in the 6ß-hydroxycortisol/cortisol ratio was estimated to be 0.91. The genetic component is likely to contribute significantly to the variability of the 6ß-hydroxycortisol/cortisol ratio, and such variability should be considered when the ratio is used to evaluate CYP3A induction or inhibition in a given ethnic population.

Key Words: CYP3A • interindividual variability • intraindividual variability

Address for reprints: Ophelia Q. P. Yin, PhD, School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong.

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