Interaction between nonsteroidal anti-inflammatory drugs and loop diuretics: modulation by sodium balance

Nonsteroidal anti-inflammatory drugs have been shown to decrease the natriuretic response to loop diuretics in many but not all studies. Recently, indomethacin was shown not to affect the natriuretic response to the new loop diuretic torasemide in healthy volunteers. Inasmuch as sodium balance has been reported to modify the effect of indomethacin on furosemide-induced natriuresis in dogs, we investigated the effect of indomethacin, under two sodium balances (50 and 150 mEq/day), on the natriuretic response to two doses of torasemide in six healthy volunteers. Under the low sodium diet, indomethacin reduced the natriuretic response to torasemide like that to furosemide. In contrast, on the normal sodium diet, indomethacin failed to affect the natriuretic response to torasemide. Indomethacin reduced base-line and diuretic-induced increase in plasma renin activity, plasma angiotensin II levels and urinary excretion of prostaglandin 6-keto F1 alpha to a similar extent under the two sodium diets. Our data show that indomethacin reduces the natriuretic response to torasemide in humans. Dietary sodium restriction is a significant determinant of the interaction between nonsteroidal anti-inflammatory drugs and loop diuretics in healthy volunteers, presumably because it allows loop diuretics to provoke an increase in renal blood flow which participates in their natriuretic action and is blocked by nonsteroidal anti-inflammatory drugs.