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:
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 |
