Diuretics

Loop Diuretics (Furosemide)

• acts in thick ascending limb of loop of Henle to block the Na+/K+/2Cl- co-transporter, preventing reabsortion of Na, K, Cl
• increase fractional excretion of Ca++ up to 30%, increase fractional excretion of Mg++ up to 60%
• used to tx hypercalcemia, edematous states ie CHF

Thiazides and Thiazide-like Diuretics (chlorothiazide)

• acts in distal convoluted tubule to block coupled Na and Cl reabsorption
• increase excretion of Na, K, Cl but less potently than loop diuretics
• reduce Ca++ excretion
• used in uncomplicated hypertension, less useful in edematous states

Distal Potassium-Sparing Diuretics (spironolactone, amiloride)

• acts in cortical collecting duct prinicpal cells on aldosterone-sensitive Na+ channel
• reduced excretion of K+, Ca++, Mg++
• first line for cirrhotic ascites, also can be used in heart failure w/ systolic dysfunction, weak diuresis so commonly used in combination with a loop/thiazide diuretic to decrease K+ loss, increase diuresis in refractory edema

Carbonic Anhydrase Inhibitors (acetazolamide)

• act in proximal tubule to inhibit bicarbonate absorption
• transient, brisk alkaline diuresis
• useful in edema w/ metabolic alkalosis to help restore acid-base balance

Osmotic Diuretics (Mannitol)

• freely filtered but poorly reabsorbed
• acts in proximal nephron and thin loops of Henle to prevent urinary concentration