Diuretics are a class of medications that promote the excretion of water and electrolytes from the body through the urine. They are primarily used to manage conditions associated with fluid retention, such as heart failure, hypertension, and certain kidney disorders.
Types of Diuretics
Diuretics are classified into several categories based on their site of action and specific mechanisms:
- Thiazide Diuretics
- Loop Diuretics
- Potassium-Sparing Diuretics
- Carbonic Anhydrase Inhibitors
- Osmotic Diuretics
Thiazide Diuretics
- Hydrochlorothiazide
- Mechanism: Inhibits sodium reabsorption in the distal convoluted tubule, increasing the excretion of sodium and water.
- Uses: Hypertension, edema associated with heart failure, hepatic cirrhosis, and chronic kidney disease.
- Dose: 12.5-50 mg orally once daily.
- Adverse Effects: Hypokalemia, hyponatremia, hypercalcemia, hyperglycemia, hyperlipidemia.
- Contraindications: Anuria, severe renal impairment, hypersensitivity to sulfonamides.
- Chlorthalidone
- Mechanism: Similar to hydrochlorothiazide but longer-acting.
- Uses: Hypertension, heart failure.
- Dose: 12.5-25 mg orally once daily.
- Adverse Effects: Similar to hydrochlorothiazide, with an increased risk of electrolyte imbalance.
- Contraindications: Similar to hydrochlorothiazide.
Loop Diuretics
- Furosemide
- Mechanism: Inhibits the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle, causing significant diuresis.
- Uses: Acute pulmonary edema, chronic heart failure, renal impairment, and edema due to liver cirrhosis.
- Dose: 20-80 mg orally once or twice daily, can be given IV in acute settings.
- Adverse Effects: Hypokalemia, hyponatremia, hypomagnesemia, dehydration, ototoxicity.
- Contraindications: Anuria, hypersensitivity to furosemide or sulfonamides.
- Bumetanide
- Mechanism: Similar to furosemide but more potent.
- Uses: Similar to furosemide.
- Dose: 0.5-2 mg orally once or twice daily, can be given IV.
- Adverse Effects: Similar to furosemide.
- Contraindications: Similar to furosemide.
Potassium-Sparing Diuretics
- Spironolactone
- Mechanism: Aldosterone antagonist that inhibits sodium reabsorption in the distal tubules and collecting ducts, promoting potassium retention.
- Uses: Heart failure, hypertension, primary hyperaldosteronism, edema.
- Dose: 25-100 mg orally once or twice daily.
- Adverse Effects: Hyperkalemia, gynecomastia, menstrual irregularities, gastrointestinal disturbances.
- Contraindications: Hyperkalemia, Addison’s disease, anuria, acute renal insufficiency.
- Amiloride
- Mechanism: Inhibits sodium channels in the distal tubules and collecting ducts, reducing potassium excretion.
- Uses: Hypertension, heart failure, used in combination with thiazide or loop diuretics to prevent hypokalemia.
- Dose: 5-20 mg orally daily.
- Adverse Effects: Hyperkalemia, nausea, vomiting.
- Contraindications: Hyperkalemia, severe renal impairment.
Carbonic Anhydrase Inhibitors
- Acetazolamide
- Mechanism: Inhibits carbonic anhydrase, reducing the reabsorption of bicarbonate in the proximal tubule, leading to increased excretion of sodium, potassium, and water.
- Uses: Glaucoma, altitude sickness, metabolic alkalosis, epilepsy.
- Dose: 250-1000 mg orally daily, in divided doses.
- Adverse Effects: Metabolic acidosis, hypokalemia, renal stones, paresthesias.
- Contraindications: Severe renal or hepatic disease, adrenal insufficiency, hyperchloremic acidosis.
Osmotic Diuretics
- Mannitol
- Mechanism: Increases the osmolarity of the glomerular filtrate, inhibiting reabsorption of water and electrolytes.
- Uses: Acute renal failure, increased intracranial pressure, increased intraocular pressure.
- Dose: 0.25-2 g/kg IV over 30-60 minutes.
- Adverse Effects: Electrolyte imbalance, dehydration, headache, nausea, vomiting.
- Contraindications: Anuria, severe dehydration, active intracranial bleeding, pulmonary edema.
Clinical Use and Guidelines
In the UK, the use of diuretics is guided by clinical guidelines from authoritative bodies such as the National Institute for Health and Care Excellence (NICE).
- Hypertension:
- Thiazide diuretics are often the first-line treatment, either alone or in combination with other antihypertensive agents.
- Heart Failure:
- Loop diuretics like furosemide are commonly used to manage fluid overload.
- Potassium-sparing diuretics such as spironolactone are used to counteract the potassium loss caused by other diuretics and for their added benefits in heart failure management.
- Renal Disorders:
- Loop diuretics are used in managing edema associated with renal impairment.
- Carbonic anhydrase inhibitors are used for specific conditions like metabolic alkalosis.
- Special Situations:
- Osmotic diuretics like mannitol are used in acute settings for managing increased intracranial or intraocular pressure.
Administration and Monitoring
Diuretics are typically administered orally, but some, like furosemide and mannitol, can be given intravenously in acute settings. Monitoring is essential to ensure efficacy and prevent adverse effects:
- Electrolytes: Regular monitoring of serum electrolytes, including sodium, potassium, and magnesium.
- Renal Function: Periodic assessment of renal function through serum creatinine and blood urea nitrogen (BUN).
- Fluid Balance: Monitoring of fluid intake and output, body weight, and signs of dehydration or fluid overload.
Adverse Effects and Contraindications
The primary adverse effects of diuretics include electrolyte imbalances and dehydration. Specific adverse effects and contraindications vary by drug class:
- Thiazides: Hypokalemia, hyponatremia, hypercalcemia, hyperglycemia, hyperlipidemia. Contraindicated in anuria, severe renal impairment.
- Loop Diuretics: Hypokalemia, hyponatremia, hypomagnesemia, dehydration, ototoxicity. Contraindicated in anuria, hypersensitivity to sulfonamides.
- Potassium-Sparing Diuretics: Hyperkalemia, gynecomastia (spironolactone). Contraindicated in hyperkalemia, Addison’s disease.
- Carbonic Anhydrase Inhibitors: Metabolic acidosis, hypokalemia, renal stones, paresthesias. Contraindicated in severe renal or hepatic disease.
- Osmotic Diuretics: Electrolyte imbalance, dehydration, headache, nausea, vomiting. Contraindicated in anuria, severe dehydration, and active intracranial bleeding.
Diuretics are vital medications in the management of hypertension, heart failure, and fluid retention associated with various medical conditions. Their use requires careful consideration of the patient’s overall health, monitoring of electrolyte levels, and awareness of potential adverse effects and contraindications.