Effects of a new diuretic (piretanide) compared with furosemide on renal diluting and concentrating mechanisms in patients with the nephrotic syndrome.

The mode and site of action of the new diuretic agent piretanide were investigated in man. The effect of a single oral dose of 12 mg was compared with that of furosemide 80 mg p.o. iin 6 patients with the nephrotic syndrome. Piretanide showed a greater diuretic and natriuretic response than furosemide during maximal water diuresis, but the effect was similar in the hydropenic state. Like furosemide, piretanide decreased free water clearance relative to delivery during water diuresis and the reabsorption of solute-free water during hydropenia. This inhibitory action on both the concentrating and diluting urinary mechanisms demonstrates an effect of piretanide localized in the ascending limb of Henle's loop. Consistent alterations in glomerulur filtration rate, renal blood flow or filtration fraction were not observed.