Diuretics Pharmacology : Classification Of Diuretics & Medicinal Uses | PDF Download

Afnan January 06, 2018


Introduction:

Diuretics or diuretic agents are the substances which enhance the urine formation and output. These substances increase the excretion of water, sodium, and chloride through urine. Diuretic agents increase the urine formation, by influencing any of the processes involved in urine formation. Diuretics are commonly called ‘water pills’.

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Uses of diuretics:

Diuretics are generally used for the treatment of disorders involving an increase in extracellular fluid volume like:
1. Hypertension
2. Congestive cardiac failure
3. Edema.
Diuretic agents prevent hypertension, congestive cardiac failure, and edema, by increasing the urinary
Output and reducing extracellular fluid (ECF) volume. Nowadays, diuretics are misused in order to reduce the body weight and keep the body slim. Even persons, Suffering from eating disorders attempt to reduce body weight by misusing the diuretics. However, prolonged use of these substances leads
To complications like syndrome of diuretic-dependent sodium retention, characterized by edema. The adverse effects depend upon the type of diuretic agents used.

Classification of diuretics agents:

Diuretics are classified into seven classes:
  1. Osmotic diuretics
  2. Diuretics which inhibit active reabsorption of electrolytes
  3. Diuretics which inhibit action of aldosterone carbonic anhydrase Inhibitors
  4. Diuretics which increase glomerular filtration rate
  5. Diuretics which inhibit secretion of ADH


Osmotic diuretics

Osmotic diuretics are the substances that induce osmotic diuresis. Osmotic diuresis is the type of diuresis that occurs because of increased osmotic pressure. Some of the osmotically active substances are not reabsorbed from renal tubules. When injected in large quantities into the body, these substances increase the osmotic pressure in the tubular fluid. The increased osmotic pressure in the tubular fluid, in turn, reduces water reabsorption. It leads to excretion of an excess of water through urine. Elevated blood sugar level in diabetes can also cause osmotic diuresis in the same manner.
Examples
  • Urea
  • Mannitol
  • isosorbide
  • Sucrose
  • Glucose.


Diuretics inhibiting active reabsorption of electrolytes in nephron

Diuretics of this type inhibits the active reabsorption of electrolytes like sodium and potassium from the renal tubular fluid. Inhibition of electrolyte reabsorption causes osmotic diuresis. These diuretic agents are of three types:

1. Loop diuretics – diuretics which inhibit the electrolyte reabsorption in thick ascending limb of Henle loop

Loop diuretics are the substances that inhibit electrolyte reabsorption in Henle loop. These diuretics inhibit the sodium and chloride reabsorption from thick ascending limb of Henle loop. So, the osmotic pressure in tubular fluid increases, leading to diuresis. The osmolarity of medullary interstitial fluid also decreases due to inhibition of sodium reabsorption into medullary interstitium. So, the medullary interstitium fails to concentrate the urine, resulting in loss of excess fluid through urine.
Examples
  • Furosemide
  • Torasemide
  • Bumetanide


2. Diuretics which inhibit active transport of electrolytes in the proximal part of distal convoluted tubule – Thiazides etc.

Diuretics of this type inhibit sodium reabsorption in the proximal part of the distal convoluted tubules. These diuretics are usually called thiazide and related diuretics.
Examples
  • Chlorothiazide
  • Metolazone
  • Benzthiazide
  • Methyl chlorothiazide
  • Chlortalidone.


3. Diuretics which inhibit active transport of electrolytes in distal part of distal convoluted tubule and collecting duct

Some of the diuretics inhibit reabsorption of sodium and excretion of potassium in the distal portion of the distal convoluted tubule and collecting duct. Such substances are called potassium-retaining diuretics or potassium-sparing diuretics.
Examples
  • Triamterene
  • Amiloride.


Agents which inhibit action of aldosterone

Some diuretics inhibit sodium reabsorption and potassium excretion in the distal convoluted tubule and
Collecting duct, by inhibiting the action of aldosterone. These substances are also called the potassium retaining diuretics or aldosterone antagonists.
Examples
  • Spironolactone
  • Eplerenone.


Drugs which inhibit activity of carbonic anhydrase

Some diuretics inhibit the activity of carbonic anhydrase in proximal convoluted tubules and prevent reabsorption of bicarbonates from renal tubules, resulting in osmotic diuresis. Such diuretic agents are called carbonic anhydrase inhibitors. Acetazolamide is a carbonic anhydrase inhibitor. Other examples are;
  • Dorzolamide
  • Methazolamide
  • Brinzolamide
  • dichlorphenamide


Drugs increasing glomerular filtration rate

Some xanthines (alkaloids, used as mild stimulants) cause diuresis by increasing the glomerular filtration rate and to some extent by decreasing the sodium reabsorption.
Examples
  • Caffeine
  • Theophylline.


Agents inhibiting secretion of antidiuretic hormone

Some diuretics produce diuresis by inhibiting the secretion of ADH.
Examples
  • Water
  • Ethanol.


Agents which inhibit antidiuretic hormone receptors

The antagonists of v2 receptors cause diuresis by inhibiting the receptors of antidiuretic hormone, thereby preventing the activity of this hormone. Examples included are;
  • Demeclocycline
  • Lithium citrate
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