DIURETIC

A 'diuretic' is any drug that elevates the rate of bodily urine excretion (diuresis). There are several categories of diuretics. All diuretics increase the excretion of water from the body, although each class of diuretic does so in a distinct way.

Contents

High ceiling loop diuretics

Thiazides

Osmotic diuretics

High Blood Glucose

Uses

Mechanism of action

External links

High ceiling loop diuretics

Drugs such as furosemide inhibit the body's ability to reabsorb sodium at the ascending loop in the kidney which leads to a retention of water in the urine as water normally follows sodium back into the extracellular fluid (ECF.) Other examples of high ceiling loop diuretics include ethacrynic acid, torasemide and bumetanide.

Thiazides

Drugs such as hydrochlorothiazide act on the distal tubule and inhibit the Na-Cl symport leading to a retention of water in the urine as water normally follows penetrating solutes.
== Potassium sparing diuretics ==
Drugs such as spironolactone are competitive antagonists of aldosterone. Aldosterone normally adds sodium channels in the principal cells of the collecting duct and late distal tubule of the nephron. Spironolactone prevents aldosterone from entering the principal cells, preventing sodium reabsorption. Other examples of potassium-sparing diuretics are amiloride and triamterine. These drugs bind to the sodium channels of the principal cells, inhibiting an aldosterone-induced increase in sodium reabsorption.

Osmotic diuretics

Compounds such as mannitol are filtered in the glomerulus, but cannot be reabsorbed. Their presence leads to an increase in the osmolarity of the filtrate. To maintain osmotic balance, water is retained in the urine.

High Blood Glucose

Glucose, like mannitol, is a sugar that can behave as an osmotic diuretic. Unlike mannitol, glucose is commonly found in the blood. However, in certain conditions such as diabetes mellitus, the concentration of glucose in the blood exceeds the maximum resorption capacity of the kidney. When this happens, glucose remains in the filtrate, leading to the osmotic retention of water in the urine. Use of some drugs, especially stimulants may also increase blood glucose and thus increase urination.

Uses

In medicine, diuretics are used to treat heart failure, liver cirrhosis, hypertension and certain kidney diseases. Some diuretics, such as acetazolamide, help to make the urine more alkaline and are helpful in increasing excretion of substances such as aspirin in cases of overdose or poisoning. Diuretics are often abused by sufferers of eating disorders, especially bulimics, in attempts at weight loss.
The antihypertensive actions of some diuretics (thiazides and loop diuretics in particular) are independent of their diuretic effect. That is, the reduction in blood pressure is not due to decreased blood volume resulting from increased urine production, but occurs through other mechanisms and at lower doses than that required to produce diuresis. Indapamide was specifically designed with this in mind, and has a larger therapeutic window for hypertension (without pronounced diuresis) than most other diuretics.

Mechanism of action

Classification of common diuretics and their mechanisms of action
Agent Group	Examples	Mechanism	Location
' -'	Ethanol, Water	inhibits vasopressin secretion
'Acidifying salts'	CaCl2, NH4Cl
'Arginine vasopressin receptor 2 antagonists'	amphotericin B, lithium citrate	inhibit vasopressin's action	collecting duct
'Aquaretics'	Goldenrod, Juniper	Increases blood flow in kidneys
'Carbonic anhydrase inhibitors'	acetazolamide, dorzolamide	inhibit H+ secretion, resultant promotion of Na+ and K+ excretion	proximal tubule
'Loop diuretics'	bumetanide, ethacrynic acid, furosemide, torsemide	inhibit the Na-K-2Cl symporter	medullary thick ascending limb
'Osmotic diuretics'	glucose (especially in uncontrolled diabetes), mannitol	promote osmotic diuresis	proximal tubule, descending limb
'Potassium-sparing diuretics'	amiloride, spironolactone, triamterene	inhibition of Na+/K+ exchange: Spironolactone inhibits aldosterone action, Amiloride inhibits epithelial sodium channels	cortical collecting ducts
'Thiazides'	bendroflumethiazide, hydrochlorothiazide	inhibit Na+/Cl- reabsorption	distal convoluted tubules
'Xanthines'	caffeine, theophylline	inhibit reabsorption of Na+, increase glomerular filtration rate	tubules

Chemically, diuretics are a diverse group of compounds that either stimulate or inhibit various hormones that naturally occur in the body to regulate urine production by the kidneys. Herbal medications are not inherently diuretics. They are more correctly called aquaretics.

External links

★ Diagram at mmi.mcgill.ca

★ Diagram at cvpharmacology.com