Metyrapone is a drug used in the diagnosis of adrenal insufficiency and occasionally in the treatment of Cushing's syndrome (hypercortisolism). Metyrapone blocks cortisol synthesis by inhibiting steroid 11β-hydroxylase. This stimulates ACTH secretion, which in turn increases plasma 11-deoxycortisol levels. Metyrapone can be used in the diagnosis of adrenal insufficiency. In patients with intact Hypothalamo-pituitary-adrenal axis, CRH and ACTH levels rise as a response to the falling cortisol levels. This results in an increase of the steroid precursors in the pathway. Metyrapone test may aid in verifying the cause of Cushing's syndrome. Most patients with pituitary dysfunction and/or pituitary microadenoma will increase ACTH secretion in response to metyrapone, while most ectopic ACTH-producing tumors will not. Pituitary macroadenomas do not always respond to metyrapone.
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