Changes of fractional renal clearance of magnesium after spironolactone administration in normal subjects.

Spironolactone, 200 mg/24 hours, was administered for 4 days to 18 clinically healthy subjects and 10 hospitalised patients with normal renal function. Changes of fractional renal clearance of magnesium before and after spironolactone administration were studied in the first group. Corresponding changes of the ratio of renal clearance of potassium to renal clearance of magnesium were studied in the second group. After spironolactone administration, fractional clearance of magnesium showed a statistically significant decrease in relation to its values before spironolactone administration, while the ratio clearance of potassium/clearance of magnesium showed no statistically significant change. The results suggest that spironolactone administration decreases the renal excretion of magnesium and potassium in an equivalent manner.