 Spironolactone is a competitive aldosterone receptor antagonist that acts on the distal convoluted tubule and collecting duct to facilitate sodium excretion while conserving potassium and hydrogen ions. Since only a minimal amount of sodium filtered by the glomerulus reaches the distal tubule, spironolactone is considered a weak diuretic. Spironolactone is primarily used with chlorothiazide for its potassium-sparing effect to reduce the need for electrolyte supplementation. There has only been one prospective, randomized, double-blind, placebo-controlled study comparing chlorothiazide with or without the addition of spironolactone in premature infants with chronic lung disease. This study demonstrated no difference between the groups in the need for electrolyte supplementation, electrolyte balance, or pulmonary function. In addition, preterm infants distal tubules may respond inadequately to aldosterone; thereby, limiting the role of spironolactone in this patient population. 