Mifepristone is a potent antagonist of glucocorticoid and progesterone receptors. It is the only drug administered to humans with these actions. Exploration of mifepristone in the treatment of Cushing's syndrome is in its infancy. The cases reviewed in this report comprise the entire medical literature. Development and availability of mifepristone has been severely restricted because of controversy surrounding its ability to function as an "abortion pill." As the political controversy abates, increasing studies of this drug may be anticipated in patients with glucocorticoid excess. Although the authors have highlighted therapeutic trials with the drug, they also note that diagnostic uses in cases of glucocorticoid excess may be of interest. Some cases of endogenous Cushing's syndrome are difficult to diagnosis and a glucocorticoid antagonist may be as useful as a glucocorticoid agonist (such as dexamethasone) in the dynamic evaluation of glandular function. In particular, mifepristone might be useful in distinguishing pituitary from occult ectopic ACTH-secreting tumors. One of the primary problems surrounding the use of mifepristone in cases of Cushing's syndrome is the long half-life of the drug and the necessity to titrate doses carefully in a manner that avoids signs and symptoms of glucocorticoid deficiency. Biochemical markers reflecting the "glucocorticoid status" of a patient would be useful for dose adjustment and monitoring and would improve the risk to benefit ratio for mifepristone treatment of Cushing's syndrome.
PIP: As a potent antagonist of glucocorticoid and progesterone receptors, mifepristone (RU-486) has potential use in the treatment of Cushing's syndrome. Initial research in this area has demonstrated that RU-486 acts as an anti-glucocorticoid by antagonizing the negative feedback on the pituitary of endogenous and exogenous glucocorticoids. Since 1985, the literature has reported four studies of the feasibility of RU-486 treatment in Cushing's syndrome patients. In the largest of these studies, 11 patients with inoperable adrenal cancer or ectopic adrenocorticotrophic hormone-secreting neoplasms received 5-22 mg/kg/day of RU-486 for 1-12 months. In seven of these patients, treatment resulted in marked improvement in the Cushingoid phenotype, psychiatric status, hypertension, and carbohydrate intolerance. Three patients discontinued RU-486 because of clinical manifestations of adrenal insufficiency. The most common side effect was nausea. Titration of RU-486 dosing remains imprecise due to the lack of an acceptable rapid biochemical measurement to monitor glucocorticoid action. Regrettably, further research in this area has been hindered by the political controversy regarding RU-486's use as an abortifacient agent.