Effect of repeated doses of hydroflumethiazide on renal excretion of electrolytes and uric acid in healthy subjects.

: Urinary excretion of electrolytes and uric acid was investigated in six healthy subjects during repeated oral administration of 100 mg hydroflumethiazide (HFT) daily for seven days, and related to urinary thiazide excretion. Mean 24 hr-urinary excretion of sodium and chloride increased 100% (P<0.02) after the first HFT-dose, whereas 24 hr-excretion values were at control level after the fourth and seventh doses. Mean 24 hr-urinary excretion of potassium was increased by 31% after the first HFT-dose (P<0.05) and by 47% after the fourth dose (P <0.05). After HFT was discontinued, mean urinary excretion rates of sodium and chloride dropped to 30% and that of potassium to 70% of control. In the state of fluid deficiency and elevated aldosterone concentration, there was a significant positive correlation between log excretion rate of HFT and excretion rate of sodium (r=0.68, P<0.002) calculated from excretion data 0–6, 6–12, and 12–14 hrs after the seventh dose. After the first dose of HFT, sodium excretion was also significantly correlated to log excretion rate of HFT (r=0.86, P<0.001) but was probably influenced by other factors as well. Mean serum concentration of uric acid increased significantly, but mean 24 hr-urinary excretion of uric acid was constant during HFT-treatment.