Paradoxical potassium excretion in response to aldosterone antagonists

The activity of two aldosterone antagonists in reversing the urinary electrolyte changes induced by the mineralocorticoid fludrocortisone was examined in healthy subjects. Between 2-10 h after treatment there were dose-related increases in sodium excretion and the urine log 10 Na/K ratio, but no significant changes in urine volume, potassium concentration, or potassium excretion. Between 12-16 h after treatment there were dose-related increases in urine sodium excretion and the log 10 Na/K ratio. Unexpectedly, there were significant dose-related increases in potassium excretion despite significant dose-related reductions in urinary potassium concentration. The paradoxical increases in potassium excretion were attributed to dose-related increases in urine volume in the same period. These observations may explain the increased potassium excretion occasionally observed during clinical use of aldosterone antagonists and suggest that potassium excretion in man is influenced by the urine flow rate.