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:

1. 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.

2. 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.

3. 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.

4. 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).

5. 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

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