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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