Diuretics and Diuresis

NEPHROLOGY, Pharmacy and Therapeutics

  • Daily weight is the best way to track successful diuresis.
  • Diuretics inhibit sodium reabsorption in specific parts of the nephron, resulting in increased urinary sodium and water excretion.
  • “Loop diuretics are the most potent diuretics.” Electrolyte & BP 2015
  • Diuretics help in the treatment of  HTN, renal failure, cirrhosis, etc.

Loop Diuretics

Types: Furosemide, torsemide, bumetanide, and ethacrynic acid are loop diuretics.
MOA: Inhibits sodium and chloride reabsorption in the thick ascending limb of the loop of Henle. It does this by inhibiting Na-K-2Cl transporters in the thick ascending limb of the loop of Henle.
Loop diuretics have a sigmoid dose-response curve with a threshold dose and ceiling dose.
PO bioavailability of furosemide is only about 50%. Remember the 2:1 ratio. IV dose is twice as potent as the oral dose. 20 mg Lasix IV is equivalent to 40 mg
Torsemide and Bumetanide have about 90% bioavailability.
If a patient has a sulfa allergy, use ethacrynic acid.
In acute CHF, IV boluses work just as well as a continuous IV infusion.
Dose equivalents: 40 mg of furosemide PO = 20 mg of furosemide IV = 20 mg torsemide PO = 1 mg bumetanide PO/IV
Lasix = Lasts six hours. You can dose furosemide every six hours.

Thiazide Diuretics

Types: Hydrochlorothiazide (HCTZ), Chlorothiazide (Diuril), Metolazone, chlorthalidone (thiazide-like).
MOA: Inhibits sodium and chloride reabsorption in the distal convoluted tubule (DCT).
Thiazides are synergistic with loop diuretics, especially in patients on long-term use of loop diuretics.
If used with a loop diuretic, give thiazide about 30 minutes before the loop diuretic.
The synergistic effect of thiazides is decreased when GFR < 30, except for Metolazone which still works even in renal insufficiency.

Potassium-Sparing Diuretics

Types: Spironolactone, Triamterene, Amiloride, Eplerenone.
MOA: Decrease sodium reabsorption in the collecting ducts.

Check out images here. See images in Basic and Clinical Pharmacology by Katzung

 

Class Types MOA Place of action in the kidneys
Loop Diuretics Furosemide, torsemide, bumetanide, and ethacrynic acid Inhibits sodium and chloride reabsorption in the thick ascending limb of the loop of Henle. Thick ascending loop limb of the loop of Henle.
 Thiazide HCTZ, Chlorothiazide,
Metolazone, chlorthalidone		 Inhibits sodium and chloride reabsorption in the distal convoluted tubule (DCT) Distal convoluted tubule.
 K-Sparing Spironolactone, Triamterene, Amiloride, Eplerenone.  Decrease sodium reabsorption in the collecting ducts Collecting ducts

 

 

Reference / Further Reading

Harlan E. Ives, MD, Ph.D. Diuretic Agents. Chapter 15. Bertram G. Katzung BG: Basic & Clinical Pharmacology, 9e.

Oh SW, Han SY. Loop Diuretics in Clinical Practice. Electrolytes & Blood Pressure : E & BP. 2015;13(1):17-21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520883/

Pocket Medicine, 5th Edition, Mark S. Sabatine.

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