Urinary excretion of 6 beta-hydroxycortisol as an in vivo marker for CYP3A induction: applications and recommendations.

Objective: To evaluate the usefulness of 6 beta-hydroxycortisol as a screen for CYP3A induction in early-phase drug development.

Methods: Five groups of 12 healthy elderly men were randomized to one of five treatment regimens: (1) 600 mg rifampin (INN, rifampicin) once daily, (2) placebo once daily, (3) 40 mg SB 216469 twice a day, (4) 60 mg SB 216469 twice a day, or (5) 40 mg SB 216469 three times a day. All medications were taken orally and administered for 7 consecutive days. Urine was collected over a 24-hour period for each subject before administration and on the last day of administration for each respective regimen for measurement of 6 beta-hydroxycortisol and 17-hydroxycorticosteroid concentrations.

Results: Subjects in the rifampin group had a significant increase from predose value in the 24-hour urinary excretion of 6 beta-hydroxycortisol and the ratio of 6 beta-hydroxycortisol to 17-hydroxycorticosteroid. All 12 subjects in the rifampin group had increases in 6 beta-hydroxycortisol excretion, whereas 11 of 12 had an increase in the ratio. The placebo and three active treatment groups did not show significant changes in either parameter.

Conclusions: Urinary excretion of 6 beta-hydroxycortisol may be useful as a screening tool in early-phase development to assess the potential for an investigational drug to induce CYP3A.