Syndrome of Mineralocorticoid Excess with Abiraterone Use

Introduction: Abiraterone is a CYP17 enzyme inhibitor which is used to treat metastatic prostate cancer. This enzyme is involved in androgen synthesis in the testes, adrenal and prostate gland. By blocking this enzyme, it decreases cortisol production and results in increased ACTH and mineralocorticoid production. Prednisone decreases the ACTH stimulation and is given concurrently with abiraterone. We present a case of a syndrome of apparent mineralocorticoid excess in abiraterone use. Case Description: A 72-year-old man with past medical history of metastatic prostate cancer on leuprolide and abiraterone and hypertension presented from his primary care clinic with routine labs with recurrent hypokalemia to 2.8. His first episode of hypokalemia had occurred 5 months prior to presentation, also found on routine labs, and managed with oral potassium supplementation, with which he remained compliant, and a reduction in HCTZ dose. Despite these changes his potassium remained at 2.6 and he was instructed to present to the emergency department (ED). While in the ED, he was noted otherwise have blood pressures of 220/110 mm Hg. Renal function was at baseline with creatinine of 0.6 mg/dl. Hypokalemia was confirmed with whole blood potassium which was 2.5. ACTH levels were noted to 71, fractional excretion of potassium was 17.29%. On further questioning, patient reported he stopped taking low dose prednisone which had been prescribed with abiraterone. During his brief admission the patient was treated with intravenous and oral potassium supplementation, initiated on spironolactone and resumed low dose prednisone. Potassium levels stabilized after 2 days, and patient was discharge on spironolactone 150 mg in addition to his prednisone. Discussion: Resistant hypertension and hypokalemia in the setting of abiraterone use can be due to syndrome of apparent mineralocorticoid excess (SAME), when there is discontinuation of low dose prednisone. Prednisone therapy results in decreasing the ACTH feedback and thereby decreases mineralocorticoid stimulation. Additionally, mineralocorticoid antagonists can be used to treat hypertension and hypokalemia . Mineralocorticoid antagonist used to suppresses aldosterone while awaiting effects of prednisone therapy in reducing ACTH drive.