Diuretic: A drug that increases urine flow. In general, diuretic agents act at the nephron to change the reabsorption of water. Many of the diuretics function by increasing sodium excretion at specific sites in the nephron. These drugs can have important actions on both Na+ and K+ excretion and retention. The clinically important diuretics include: loop diuretics (furosemide, buetanide, ethacrynic acid), thiazides (hydrochlorothiazide, chlorthalidone) and K+ sparing diuretics (amiloride, triamterene, spironolactone). Understanding, renal physiology is critical to appreciating the diverse mechanisms of action of the diuretics.