Low-dose segmental blockade of the nephron rather than high-dose diuretic monotherapy

The specific renal effect of diuretics is due to the fact that their concentrations is almost 100-fold greater in the renal tubule than in the plasma. The function of the different segments of the nephron may be altered following changes in the effective arterial blood volume (EABV) and the extracellular fluid volume (ECFV). In diseases with reduced EABV, e.g., congestive heart failure, decompensated cirrhosis of the liver, and the nephrotic syndrome, proximal tubular hyperreabsorption of sodium occurs, leaving only a low Na+ load in the distal segments of the nephron, the site of diuretic action. Clinically, the response to diuretics is reduced or resistance to diuretics may even ensue, which can be predicted by a FENa < 0.2%. Resistance to diuretics can be overcome by short-term comedication with acetazolamide, which increases Na+ delivery to the site of action of the other diuretics used concomitantly. In states with increased ECFV, e.g. in chronic renal failure, there is distal tubular Na+ rejection, leading to a greater increase in FENa the more GFR is reduced. The remaining intact nephrons present a relatively increased response to diuretics. The efficacy of diuretic treatment in renal failure can be optimised by combining loop diuretics with thiazides. In conclusion, low-dose combination therapy, inducing "segmental blockade of the nephron", meets the functional changes along the nephron. It is therefore more effective and safer than high-dose monotherapy.