Hypokalemia associated with mifepristone use in the treatment of Cushing's syndrome

Summary: Mifepristone is a promising option for the management of hypercortisolism associated with hyperglycemia. However, its use may result in serious electrolyte imbalances, especially during dose escalation. In our patient with adrenocorticotropic hormone-independent macro-nodular adrenal hyperplasia, unilateral adrenalectomy resulted in biochemical and clinical improvement, but subclinical hypercortisolism persisted following adrenalectomy. She was started on mifepristone. Unfortunately, she missed her follow-up appointments following dosage escalation and required hospitalization at an intensive care level for severe refractory hypokalemia.

Learning points: Mifepristone, a potent antagonist of glucocorticoid receptors, has a high risk of adrenal insufficiency, despite high cortisol levels. Mifepristone is associated with hypokalemia due to spill-over effect of cortisol on unopposed mineralocorticoid receptors. Given the lack of a biochemical parameter to assess improvement, the dosing of mifepristone is based on clinical progress. Patients on mifepristone require anticipation of toxicity, especially when the dose is escalated. The half-life of mifepristone is 85 h, requiring prolonged monitoring for toxicity, even after the medication is held.