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Classification of Diuretics

Diuretica

For medical students2 min readUpdated 2026-10-10

Diuretics are classified according to their primary mechanism of action and site of action along different segments of the nephron. Understanding these pharmacological groups is essential for mastering body fluid and electrolyte regulation.

Site of loop diureticsThick ascending limb of the loop of Henle

Loop agentsFurosemide, bumetanide, ethacrynic acid

Thiazide agentsHydrochlorothiazide, cyclopenthiazide

Potassium-sparingSpironolactone, triamterene, amiloride

Physiological Basis of Diuresis and the Role of ADH

Water reabsorption regulation is closely tied to the structure of the collecting ducts and their principal cell epithelium. A key role in this process is played by antidiuretic hormone (ADH), which controls the water permeability of cell membranes.

The hormone regulates the number of water channels—aquaporins (type AQP2)—on the apical membrane.
In the presence of ADH, these water channels are inserted into the membrane, facilitating active water reabsorption.
Hormone deficiency or genetic defects in aquaporins lead to conditions such as diabetes insipidus, in which the body loses its ability to concentrate urine.

Group I: Agents Affecting Tubular Epithelium

This large group encompasses drugs acting on transport systems in specific nephron segments:

Loop diuretics act in the thick ascending limb of the loop of Henle by blocking the $Na^+-K^+$ cotransporter. This group includes furosemide, bumetanide, and ethacrynic acid.
Thiazide and thiazide-like agents affect the early distal convoluted tubule by inhibiting the $Na^+-Cl^-$ cotransporter. Examples include hydrochlorothiazide, indapamide, chlortalidone, and others.
Potassium-sparing drugs act in the late distal convoluted tubule and collecting ducts.

Potassium-Sparing Diuretics and Other Groups

Drugs that conserve potassium ions in the body are subdivided based on their intracellular mechanisms:

Sodium channel blockers (triamterene, amiloride) act directly on epithelial sodium channels (ENaC).
Aldosterone antagonists (spironolactone, eplerenone) block mineralocorticoid receptors.

In addition to these groups, classification includes osmotic diuretics and miscellaneous agents, among which are carbonic anhydrase inhibitors (acetazolamide) and xanthine derivatives (aminophylline).

Mnemonic

Loop of Henle = loop diuretics (furosemide); distal convoluted tubule = thiazides; collecting ducts = potassium-sparing (spironolactone).

Frequently asked questions

What are the adverse effects and complications of loop diuretics?

The primary adverse effects and complications of loop diuretics include electrolyte disturbances and hemodynamic shifts.

Electrolyte depletion — drugs cause hypokalemia and hypomagnesemia.
Renal hypoperfusion — occurs if furosemide is administered in the setting of hypovolemia.
Thromboembolic complications — the risk increases significantly when the drug is used under conditions of hypovolemia.

To correct electrolyte imbalances, combination with potassium and magnesium supplements or potassium-magnesium-sparing diuretics is required. If serum potassium drops below 3.0 mmol/L, furosemide should be withheld.

What are the indications and contraindications for thiazide diuretics?

Thiazide diuretics are used to treat cardiovascular diseases and endocrine disorders, but have restrictions in gout. Indications:

Hypertension — serving as foundational agents and first-line monotherapy in early stages.
Heart failure — used for symptomatic treatment and relief of congestion (edema, dyspnea).
Diabetes insipidus — utilized due to their paradoxical antidiuretic effect.

Contraindications:

Acute gout attack — hydrochlorothiazide may be contraindicated during acute flares because it can cause uric acid retention in the body (hyperuricemia).

Where in the nephron do loop diuretics act?

Loop diuretics act in the thick ascending limb of the loop of Henle, where they block the $Na^+-K^+$ cotransporter.

Which drugs are classified as sodium channel blockers?

Sodium channel blockers include triamterene and amiloride, which act directly on epithelial sodium channels (ENaC).

What is the function of antidiuretic hormone?

ADH regulates the water permeability of collecting duct cell membranes by controlling the number of water channels, specifically aquaporins (AQP2).

Go deeper

Genetic polymorphism of aquaporins in diabetes insipidus
Molecular mechanisms of $Na^+-K^+$ and $Na^+-Cl^-$ cotransporters
Pharmacological differences between thiazide and thiazide-like diuretics
The role of mineralocorticoid receptors in the action of aldosterone antagonists
Specific effects of carbonic anhydrase inhibitors and xanthines