Diuretics Medicines Information

 

Diuretics are commonly defined as drugs that increase the amount of urine produced by the kidneys. A precise definition is that diuretics are agents which augment the renal excretion of sodium and either chloride or bicarbonate primarily, and water excretion secondarily. Clinically diuretics are the mainstay of treatment of hypertension and edematous states like congestive heart failure, cirrhosis with ascites, nephritic edema, and edema or pregnancy.

Classification Of Diuretics

Although these drugs vary in their chemical structure and mechanisms of action, almost all of them interfere with the tubular reabsorption of sodium.

INDIVIDUAL AGENTS BENZOTHIADIAZIDES (THIAZIDES)

The Thiazides are related chemically to the sulphonamides, but have no antibacterial activity. The thiazide also posses some carbonic anhydrase inhibiting activity. Most of these diuretics are derived from benzothiadiazine and thus known and "thiazide".
The Thiazides have an antihypertensive action. It is of interest here to note that the non-diuretic thiazide, diazoxide, has a potent hypotensive effect without having any renal action.

HIGH-CEILING OR LOOP DIURETICS l

Frusemide, bumetanide and ethacrynic acid have been labeled as "high-ceiling" or "loop diuretics", because the inhibit the sodium and chloride reabsorption in the thick segment of the ascending limb of the loop of Henle as well as in the proximal convoluted tubule, and the distal diluting site. Thus they are very potent diuretics, and induce a dramatic and copious flow of urine rich in sodium chloride.

CARBONIC ANHYDRASE INHIBITORS

Acetazolamide is a sulphonamide and is the prototype carbonic anhydrase inhibitor. Carbonic anhydrase inhibitors have a limited use as diuretics.

POTASSIUM-SPARING DIURETICS

The potassium-sparing diuretics, spironolactone, triamterene and amiloride, interfere with sodium reabsorption at the distal exchange sites, and promote sodium excretion while potassium is conserved. Their major use is in conjunction with the thiazide or loop diuretics. Such a combined therapy reduces potassium loss, minimizes alkalosis, and is sometimes effective in refractory edema. 
Spironolactone : Spironolactone is an aldosterone antagonist. Aldosterone is an adrenal mineral corticoid responsible for the main of electrolyte balance in the body.
Triamterene : Triamterene is a nonsteroidal compound, which produces a spironolactone-like effect by acting on the distal tubule to increase Na+, C1- and H2CO3 loss and conserve K’. But it is not an aldosterone antagonist.
Amiloride: Amiloride is an organic base and has renal actions like triamterene. Its mode of action is incompletely understood. It has no aldosterone antagonistic activity.

OSMOTIC DIURETICS

Osmotic diuretics are non-electrolytes, which are freely filtered at the glomerulus, and are not significantly reabsorbed from the tubules, and there presence in the urine cause increase in the excreted electrolytes and volume flow.
Mannitol: This osmotic diuretic is administered intravenously, and is useful for the prophylaxis of acute renal failure. It is also used to reduce intraocular pressure and vitreous volume prior to ocular surgery; to reduce intracranial pressure in patients of cerebral edema; and to promote excretion of toxic substances.
Urea: Urea also is administered intravenously, and tends to draw fluid from the extracellular space into the blood. Urea is useful for reducing a raised cerebrospinal fluid pressure during neurosurgical operations and cerebral edema following head injury.
Glycerol
Glycerol is of particular use prior to ophthalmological procedures to reduce intraocular pressure.
Isosorbide
Isosorbide is available as an oral solution (45%) for reduction of intraocular pressure prior to, or following eye surgery for glaucoma or cataract, or to check an acute attack of glaucoma.

METHYLXANTHINES

The xanthenes (theophylline, theobromine, caffeine) have a weak diuretic activity Aminophylline (theophylline ethylenedianine) is the most used member.

THERAPEUTIC USES OF DIURETICS

1. Congestive Heart Failure (CHF). Digitalis is used in adequate doses to increase the cardiac output, and improve renal hemodynamic, with results in diuresis. Dietary sodium intake is restricted.
2. Essential hypertension. The thiazide usually serve as primary antihypertensive agents
3. Hepatic cirrhosis with ascites. Potassium-sparing diuretics like spironolactone may be employed. If spironolactone alone fails, then a thiazide diuretic can be added cautiously.
4. Nephrotic syndrome. Dietary sodium restriction may be combined with a thiazide diuretic, adding spironolactone to control secondary hyperaldosteronism.
5. Chronic renal failure. Careful attention to salt and water balance is required. A loop diuretic like frusemide may be useful in controlling both edema and hypertension.