Diuretics are medications that promote the excretion of water and electrolytes by the kidneys, increasing urine output.
They are used in conditions like hypertension, heart failure, edema, and certain renal disorders.
Classes of Diuretics:
Thiazide Diuretics:
Examples: Hydrochlorothiazide, Chlorthalidone, Indapamide.
Mechanism:
Inhibit the sodium-chloride symporter in the distal convoluted tubule, reducing sodium and chloride reabsorption.
Result in increased excretion of sodium, chloride, potassium, and water.
Uses: Hypertension, mild to moderate edema (e.g., in heart failure), nephrolithiasis prevention.
Side Effects: Hypokalemia, hyponatremia, hypercalcemia, hyperlipidemia, hyperglycemia, hyperuricemia, hypotension.
Loop Diuretics:
Examples: Furosemide, Bumetanide, Torsemide.
Mechanism:
Inhibit the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle, leading to significant excretion of sodium, chloride, potassium, calcium, and magnesium.
Uses: Acute and chronic heart failure, pulmonary edema, renal dysfunction, hypercalcemia.
Side Effects: Hypokalemia, hyponatremia, hypomagnesemia, hypocalcemia, ototoxicity (especially with high doses or rapid IV administration), dehydration, hypotension.
Potassium-Sparing Diuretics:
Subclasses:
A) Aldosterone Antagonists:
Examples: Spironolactone, Eplerenone.
Mechanism: Block aldosterone receptors in the collecting ducts, reducing sodium reabsorption and potassium excretion.
Uses: Heart failure, hypertension, primary hyperaldosteronism, add-on therapy in loop/thiazide diuretic regimens.
Side Effects: Hyperkalemia, gynecomastia (especially with spironolactone), menstrual irregularities, impotence.
B) Epithelial Sodium Channel (ENaC) Blockers:
Examples: Amiloride, Triamterene.
Mechanism: Directly inhibit sodium reabsorption in the collecting ducts, reducing potassium excretion.
Uses: Hypertension, heart failure, adjunctive therapy with other diuretics.
Side Effects: Hyperkalemia, gastrointestinal disturbances, dizziness.
Carbonic Anhydrase Inhibitors:
Examples: Acetazolamide, Methazolamide.
Mechanism: Inhibit carbonic anhydrase in the proximal tubule, reducing bicarbonate reabsorption, leading to excretion of sodium, bicarbonate, potassium, and water.
Uses: Glaucoma, metabolic alkalosis correction, altitude sickness prophylaxis, certain types of seizures.
Side Effects: Metabolic acidosis, hypokalemia, paresthesia, kidney stones, diuresis.
Osmotic Diuretics:
Examples: Mannitol, Glycerin.
Mechanism: Increase osmolarity of the glomerular filtrate, preventing water reabsorption in the proximal tubule and descending limb of the loop of Henle.
Uses: Cerebral edema, elevated intraocular pressure, acute renal failure prevention (during certain surgeries), osmotic therapy in certain poisonings.
Side Effects: Fluid and electrolyte imbalance, dehydration, hyperosmolarity, pulmonary edema, renal dysfunction.
Clinical Considerations:
Electrolyte Monitoring: Regular monitoring of potassium, sodium, magnesium, and calcium levels is essential, especially with loop and thiazide diuretics.
Renal Function: Diuretics can affect renal perfusion; kidney function should be monitored.
Blood Pressure Management: Diuretics are first-line for hypertension; choice depends on patient comorbidities.
Combination Therapy: Often used in combination to balance electrolyte effects (e.g., thiazides with potassium-sparing diuretics).