Indomethacin can antagonize the diuretic action of loop diuretics by:
Loop diuretics release PGs that induce intrarenal hemodynamic changes which secondarily affect salt output. Indomethacin and other NSAIDs inhibit the formation of PG. Therefore, NSAIDs blunt the action of loop diuretics.
Preventing prostaglandin mediated intrarenal-hemodynamic actions
Blocking the action in ascending limb of loop of Henle
Enhancing salt and water reabsorption in distal tubules
Increasing aldosterone secretion
Kidney