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Diuretics: Overview and Classification

  • Diuretics are a class of medications that promote the excretion of water and electrolytes (such as sodium and potassium) through the kidneys.

  • They are primarily used to manage conditions like hypertension (high blood pressure), heart failure, kidney disorders, and certain cases of edema (fluid retention).

  • By increasing urine output, diuretics help reduce blood volume, thereby lowering blood pressure and decreasing the workload on the heart.

Classification of Diuretics

  • Diuretics can be categorized based on their mechanism of action and the specific segment of the nephron (the functional unit of the kidney) they act upon.

  • Below is a concise classification of diuretics along with common examples and their primary mechanisms:

Classification of Diuretics
Classification of Diuretics

Carbonic Anhydrase Inhibitors

Examples:
  • Acetazolamide

  • Methazolamide

  • Dichlorphenamide

Mechanism of Action:
  • Inhibit the enzyme carbonic anhydrase in the proximal tubule of the nephron.

  • Reduce reabsorption of bicarbonate, leading to increased excretion of bicarbonate, sodium, potassium, and water.

Clinical Uses:
  • Treatment of glaucoma.

  • Prevention of altitude sickness.

  • Metabolic alkalosis.

Thiazide Diuretics

Examples:
  • Chlorthiazide

  • Hydrochlorothiazide

  • Hydroflumethiazide

  • Cyclothiazide

Mechanism of Action:

  • Act on the distal convoluted tubule.

  • Inhibit the sodium-chloride symporter, reducing sodium and chloride reabsorption.

  • Increase excretion of sodium, chloride, and water, while promoting potassium retention.

Clinical Uses:

  • Hypertension management.

  • Edema associated with heart failure or nephrotic syndrome.

  • Prevention of calcium-containing kidney stones.

Loop Diuretics

Examples:

  • Furosemide

  • Bumetanide

  • Ethacrynic acid

Mechanism of Action:

  • Target the ascending limb of the loop of Henle.

  • Inhibit the sodium-potassium-chloride (Na⁺-K⁺-2Cl⁻) cotransporter.

  • Significantly increase excretion of sodium, chloride, potassium, calcium, and magnesium.

Clinical Uses:

  • Acute and chronic heart failure.

  • Pulmonary edema.

  • Hypertension.

  • Acute kidney failure.

Potassium-Sparing Diuretics

Examples:
  • Spironolactone

  • Triamterene

  • Amiloride

Mechanism of Action:
  • Act on the collecting ducts and late distal tubule.

  • Spironolactone: Aldosterone receptor antagonists; block sodium reabsorption and potassium excretion.

  • Triamterene and Amiloride: Inhibit epithelial sodium channels (ENaC), reducing sodium reabsorption and potassium loss.

Clinical Uses:

  • Heart failure.

  • Hypertension.

  • Prevention of hypokalemia in patients taking other diuretics.

  • Primary hyperaldosteronism (Spironolactone).

Osmotic Diuretics

Examples:

  • Mannitol

Mechanism of Action:
  • Remain in the lumen of the nephron and inhibit water reabsorption by increasing the osmolarity of the filtrate.

  • Do not undergo significant reabsorption, thus drawing water into the urine.

Clinical Uses:

  • Reduction of intracranial pressure in cases of cerebral edema.

  • Treatment of acute kidney failure.

  • Prevention of renal toxicity in certain poisoning cases.

Summary Table

Carbonic Anhydrase Inhibitors

Acetazolamide, Methazolamide, Dichlorphenamide

Inhibit carbonic anhydrase in proximal tubule; increase excretion of bicarbonate, sodium, potassium, water

Category

Medications

Primary Mechanism

Thiazide Diuretics

Chlorthiazide, Hydrochlorothiazide, Hydroflumethiazide, Cyclothiazide

Inhibit Na⁺-Cl⁻ symporter in distal convoluted tubule; increase excretion of sodium, chloride, water

Loop Diuretics

Furosemide, Bumetanide, Ethacrynic acid

Inhibit Na⁺-K⁺-2Cl⁻ cotransporter in ascending limb of loop of Henle; increase excretion of Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺

Potassium-Sparing Diuretics

Spironolactone, Triamterene, Amiloride

Spironolactone: Aldosterone antagonists; Triamterene & Amiloride: ENaC inhibitors; reduce Na⁺ reabsorption and K⁺ loss

Osmotic Diuretics

Mannitol

Increase osmolarity of filtrate; inhibit water reabsorption

diuretics
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