Relative potency of amiloride and spironolactone in healthy man

The renal antimineralocorticoid activity of single oral doses of amiloride, a physiologic aldosterone antagonist, was compared to that of spironolactone, a competitive aldosterone antagonist, in 12 healthy men pretreated with fludrocortisone. For up to 20 hr amiloride induced linear log dose-urinary electrolyte response relationships but spironolactone dose-response trends were demonstrated only in the period from 10 to 20 hr after treatment. In this period, the best estimate of the potency of amiloride relative to spironolactone for urine log10 10 Na/K was 36 (95% confidence limits 23 to 69). The fludrocortisone model seems appropriate for quantitative comparisons of physiologic and competitive aldosterone antagonists, but does not indicate therapeutic relative potency.