52yo man comes to the physician for a f/up exam. he has a 4y hx of htn and a 1y hx of hypokalemia. current meds include labetolol, enalapril and kcl. his bp is 154/90. the remainder of the exam shows no abnormalities. his fasting serum aldosterone: renin ratio is increased. a ct scan shows a 1cm l adrenal mass. adrenal vein sampling before and after administration of acth shows b/l hypersecretion of aldosterone. which of the following is the most appropriate next step in management?
a. candesartan therapy
b. furosemide therapy
c. spironolactone therapy
d. b/l adrenalectomy
e. u/l adrenalectomy