Potential use of ketoconazole in a dynamic endocrine test to differentiate between biological outliers and testosterone use by athletes.

Determination of the ratio of testosterone to epitestosterone (T/E) in urine is used to detect testosterone administration in athletes, with a ratio > 6 considered as evidence of an offense. We show that administration of ketoconazole, which inhibits testosterone biosynthesis, may be useful for differentiating between an athlete who is using testosterone and one who naturally gives a ratio > 6. In a control subject pretreated with testosterone, ketoconazole caused the ratio to increase; conversely, it caused a decrease in the ratio in an athlete under investigation. Repeated administration of ketoconazole to two normal men caused a decrease in the ratio due to a large decrease in the urinary excretion rate of testosterone relative to epitestosterone. Stimulation with human chorionic gonadotropin exacerbated the differences in excretion rates. A single administration of ketoconazole to six normal men caused the T/E ratios to decrease significantly within 8 h, a suitable time scale for use in a dynamic test.