Bioassay of a new aldosterone antagonist and evaluation of a simple method of quantitative comparison

The renal antimineralocorticoid activity of single oral doses of a new aldosterone antagonist OH OPC(ME)-K was compared to that of spironolactone in two studies in healthy men. OH OPC(ME)-K reversed the urinary electrolyte response to fludrocortisone in the period up to 16 hr after treatment, but it was less potent than spironolactone on a weight basis. The best estimate of the relative potency of OH OPC(ME)-K: spironolactone (derived from a simple protocol using equal single doses of the two drugs) was 0.60:1 (95% confidence limits 0.24:1 to 1.42:1), in good agreement with the estimate from a more complex three-dose parallel-line bioassay (0.61:1, 95% confidence limits 0.48:1 to 0.79:1). The results of simple single-dose studies can be used, with certain assumptions, to provide a useful estimate of the relative potency of new aldosterone antagonists at an early stage of development.

Antagonism of endogenous mineralocorticoids in normal subjects by prorenoate potassium and spironolactone

The pharmacological activity of single oral doses of a new aldosterone antagonist, prorenoate potassium, has been compared with spironolactone and placebo in a balanced double-blind crossover study in six healthy subject. Endogenous mineralocorticoids were stimulated by administration of frusemide followed by dietary sodium restriction, and the urinary excretion of electrolytes in response to prorenoate potassium, spironolactone and placebo was measured over a 24 hour period. Significant activity of prorenoate potassium and spironolactone was observed between 2 - 24 hours after medication, with peak activity at 6 - 8 hours. The active drugs significantly increased sodium excretion and the sodium : potassium (Na/K) ratio, but changes in potassium excretion were not significant. The total urine Na/K response to prorenoate potassium 45 mg was significantly greater than to spironolactone 100 mg.