Thirty-three hypertensive patients with a wide range of renal function were studied during initiation of angiotensin-converting enzyme inhibition with captopril to evaluate changes in potassium levels concomitant with reduction of aldosterone excretion. Ten patients (Group I) with low levels of plasma renin activity had no change in either aldosterone excretion or potassium during the first week of therapy. Twenty-three other patients (Group II) had decreased aldosterone excretion of an average of 63 percent, often reversing secondary hyperaldosteronism. This was associated with a rise in serum potassium from 3.6 ± 0.1 to 4.4 ± 0.1 mEq/liter (p < 0.001). Serum potassium levels during captopril therapy were inversely related to glomerular filtration rate (creatinine clearance) and transiently exceeded 6.0 mEq/liter in markedly azotemic subjects. Despite rising potassium levels, nine patients had reduced aldosterone excretion to subnormal levels, sometimes for many months. During initiation of converting-enzyme inhibition, potassium-sparing agents and supplements should be discontinued and serum potassium levels should be monitored closely, particularly in patients with impaired renal function.
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