Differential effects of direct antagonism of AII compared to ACE inhibitors on serum potassium levels and azotemia in patients with severe congestive heart failure.

OBJECTIVES. The present study was undertaken to determine if direct blockade of angiotensin II receptors by losartan potassium as compared to ACE inhibition might result in greater tolerability in patients with congestive heart failure in whom ACE inhibition resulted in hyperkalemia and azotemia. BACKGROUND. Blockade of angiotensin II receptors by losartan potassium may produce similar benefits in congestive heart failure as ACE inhibition. However, some observations suggest losartan potassium may have different effects on renal function than ACE inhibition. METHODS. Five consecutive patients with severe congestive heart failure were identified in whom treatment with ACE inhibition was complicated by hyperkalemia (K>5.7) and azotemia. In three of these patients losartan potassium was substituted for ACE inhibition while losartan potassium was added to treatment with ACE inhibition in the remaining two. The mean of four serial values of potassium, blood urea nitrogen, and creatinine were compared before and after change in treatment using a two-tailed t test. RESULTS. The addition or substitution of losartan potassium resulted in statistically insignificant reductions in blood urea nitrogen and creatinine and a significant reduction in potassium from 5.7+/-0.1 to 4.9+/-0.3, p<0.03. Two patients who had required kayexalate were withdrawn. In all patients, hyperkalemia resolved and did not reoccur. CONCLUSIONS. There appear to be fundamental differences between the effects of losartan potassium and ACE inhibitors on potassium excretion in congestive heart failure patients with mild to moderate renal insufficiency. Losartan potassium may also be associated with less azotemia in such patients. These differences may have important clinical implications, particularly in the subset of patients in whom ACE inhibition is poorly tolerated as a result of hyperkalemia and azotemia. (c)2000 by CHF, Inc.