The pharmacodynamics of single doses of prorenoate potasssium and spironolactone in fludrocortisone treated normal subjects.

1 The pharmacodynamic profile of single oral doses of prorenoate potassium (40 mg) and spironolactone (100 mg), as judged by reversal of the effects of fludrocostisone on the urinary electrolyte composition, was compared to that of placebo in a double-blind crossover study in six healthy subjects. 2 Both drugs showed evidence of significant activity in all periods between 2-16 h after treatment, and the time course of their activity was very similar. 3 In the total 24 h period after treatment both drugs significantly increased sodium excretion, the Na/K ratio and the log 10 Na/K ratio over placebo values, and urine potassium concentration was significantly reduced. Changes in urine volume and in potassium excretion were not significant. 4 The responses to prorenoate potassium (40 mg) were not significantly different from those to spironolactone 100 mg), and were very similar as judged by the urine log 10 Na/K ratio, indicating that the two drugs were approximately equiactive at these doses. 5 Reductions in urinary potassium excretion, when expressed in relation to the amount of sodium excreted, were significantly larger after prorenoate potassium than after spironolactone, confirming a qualitative difference in the pharmacological activity of the two drugs which has been reported previously.