Diuretics are drugs that increase urine formation and promote the excretion of water and electrolytes (mainly sodium). They are widely used in the management of hypertension, kidney disorders, edema, and heart failure.
How Do Diuretics Work?
Diuretics act on different parts of the nephron in the kidneys. By blocking sodium reabsorption, they increase urinary output. The more sodium excreted, the more water is lost along with it.
Classification of Diuretics
Diuretics are categorized based on their site and mechanism of action:
1. Thiazide Diuretics
- Hydrochlorothiazide (HCTZ)
- Chlorthalidone
- Metolazone
Mechanism
Act on the distal convoluted tubule to block Na⁺/Cl⁻ cotransporter, increasing sodium and water excretion.
Uses
- Hypertension (first-line)
- Mild edema
- Heart failure
Side Effects
- Hypokalemia
- Hyperuricemia
- Hyperglycemia
2. Loop Diuretics
- Furosemide
- Bumetanide
- Torsemide
Mechanism
Act on the thick ascending limb of the loop of Henle by blocking the Na⁺/K⁺/2Cl⁻ transporter. They are the most potent diuretics.
Uses
- Acute pulmonary edema
- Congestive heart failure
- Renal failure
- Hypercalcemia
Side Effects
- Severe hypokalemia
- Dehydration
- Ototoxicity (hearing issues)
3. Potassium-Sparing Diuretics
- Spironolactone
- Eplerenone
- Amiloride
- Triamterene
Mechanism
- Spironolactone, Eplerenone: Aldosterone antagonists in the distal tubule
- Amiloride, Triamterene: Block Na⁺ channels in collecting duct
Uses
- Heart failure
- Hypertension (combined with thiazides)
- Ascites
Side Effects
- Hyperkalemia
- Gynecomastia (spironolactone)
4. Carbonic Anhydrase Inhibitors
- Acetazolamide
Mechanism
Inhibit carbonic anhydrase in the proximal tubule, decreasing bicarbonate reabsorption.
Uses
- Glaucoma
- Altitude sickness
- Metabolic alkalosis
Side Effects
- Metabolic acidosis
- Kidney stones
5. Osmotic Diuretics
- Mannitol
Mechanism
Increases osmotic pressure in renal tubules → prevents water reabsorption.
Uses
- Raised intracranial pressure
- Cerebral edema
- Acute renal failure
Side Effects
- Dehydration
- Pulmonary edema
Clinical Uses of Diuretics
- Hypertension
- Heart failure
- Edema due to liver or kidney disease
- Glaucoma
- Acute renal failure
- Hypercalcemia (loop diuretics)
Adverse Effects (General)
- Electrolyte imbalance (Na⁺, K⁺, Mg²⁺ loss)
- Dehydration
- Metabolic alkalosis (thiazides & loops)
- Hyperkalemia (potassium-sparing diuretics)
Summary Table
| Class | Site of Action | Examples | Main Uses |
|---|---|---|---|
| Thiazides | Distal tubule | HCTZ, Chlorthalidone | Hypertension |
| Loop Diuretics | Loop of Henle | Furosemide | Pulmonary edema |
| K⁺-Sparing | Collecting duct | Spironolactone, Amiloride | Heart failure |
| Carbonic Anhydrase Inhibitors | Proximal tubule | Acetazolamide | Glaucoma |
| Osmotic | Throughout nephron | Mannitol | ICP, cerebral edema |
Detailed Notes:
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