Potassium-sparing diuretics such as the triamterene component of a mixed thiazide - potassium-sparing diuretic combination can cause hyperkalemia. All of the other agents, including hydrochlorothiazide (alone), furosemide, prazosin, nifedipine, and alpha-methyldopa are safe to use in chronic renal failure. The dosage of all of these agents, however, should be reduced when renal failure supervenes. In addition to the potassium-sparing diuretics, the ACE inhibitors and angiotensin receptor blockers can also significantly raise the serum potassium level. Thus they must never be used in patients with chronic renal failure who are receiving any kind of potassium-sparing diuretic or other potassium supplement for any reason. Second, they are at least relatively contraindicated when patients develop the degree of renal insufficiency necessary to produce chronic renal failure. Ref: Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy, 3rd Ed, Page 442-446