Ketoconazole inhibits cortisol secretion of an adrenal adenoma in vivo and in vitro.

Ketoconazole (Nizoral), an oral broad spectrum antifungal agent, inhibits ergosterol synthesis in fungi and cholesterol synthesis in mammalian cells by inhibition of the 14-demethylation of lanosterol. After a blunted cortisol response to ACTH in normal men after ketoconazole has been shown by others we studied the influence of the antifungal agent on the cortisol secretion in a patient with a cortisol producing adrenal adenoma in vivo and in vitro. Repeated oral doses of ketoconazole (200 mg every 5 h over a period of 48 h) induced a reproducible clear-cut fall of serum cortisol levels under 2.5 micrograms/dl. The inhibitory effect of the cortisol secretion could be detected first 5 h after the first dose, 9 h after the last dose cortisol levels recovered. In addition the inhibitory effect of ketoconazole on cortisol secretion could be reproduced in vitro by incubating tissue slices of the excised adrenal tumor together with the antifungal agent in concentrations equivalent to therapeutic serum levels. These findings emphasize that patients with an autonomous cortisol production caused by an adrenal tumor are prone to dangerous hypoadrenalism if treated with ketoconazole.