Saturday, October 10, 2015

DIURETICS an overview

The amount of fluid (water) retained by the body is controlled primarily by the kidneys. This occurs due to the kidney's ability to control the retention and elimination of sodium and chloride, because the amounts of sodium, chloride, and water in the body are carefully balanced. Thus, if sodium and chloride are eliminated from the body, water also is eliminated. Conversely, if sodium and chloride are retained by the body, so is water.

The elimination of sodium, chloride, and water from the body is somewhat complex. In the kidneys, sodium, chloride, and other small molecules are filtered out of the blood and into the tubules of the kidney where urine is formed. Most of the sodium, chloride, and water are reabsorbed into the blood before the filtered fluid leaves the kidney in the form of urine. To make matters even more complex, there are different mechanisms that are active in different parts of the tubules that affect the reabsorption of sodium and chloride.

A diuretic is any substance that promotes the production of urine. This includes forced diuresis. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way. Alternatively, an antidiuretic such as vasopressin, or antidiuretic hormone, is an agent or drug which reduces the excretion of water in urine.

Uses of Diuretics

Diuretics are used with other types of medications (adjunctive therapy) in edema associated with congestive heart failure (CHF), cirrhosis of the liver, and corticosteroid and estrogen therapy. Also are useful in edema caused by renal dysfunction (for example, nephrotic syndrome, acute glomerulo nephritis, and chronic renal failure).

Diuretics are used to lower urinary calcium excretion, making them useful in preventing calcium-containing kidney stones and as the sole therapeutic agents to treat hypertension. Diuretics can also be used in combination with other antihypertensive drugs to treat more severe forms of hypertension. Diuretics (specifically the carbonic anhydrase inhibitors) are used as adjunctive treatment of chronic simple (open-angle) glaucoma and secondary glaucoma

CLASSIFICATION
1.      Acting at proximal convoluted tubules
i. Osmotic diuretics - Osmotic diuretics are substances that increase osmolality but have limited tubular epithelial cell permeability. They work primarily by expanding extracellular fluid and plasma volume, therefore increasing blood flow to the kidney,particularly the peritubular capillaries.
·       Glycerin, Mannitole, Isosorbide and Urea
             ii. Carbonic anhydrase inhibitors - Carbonic anhydrase                                     inhibitors inhibit the enzyme carbonic anhydrase which is                        found in the proximal convoluted tubule. This results in                              several effects including bicarbonate accumulation in the                            urine and decreased sodium absorption.
·       Acetazolamide, Methazolamide
iii.    Acidifying drugs
·       Ammonium chloride
iv.  Others
like tea, coffee, Theophylline, etc.

       2.Acting at loop of Henle
i.    Loop diuretics - Loop diuretics, such as furosemide, inhibit the body's ability to reabsorb sodium at the ascending loop in the nephron, which leads to an excretion of water in the urine, whereas water normally follows sodium back into the extracellular fluid.
·       Furosemide, Torsemide, Ethacrynic acid and Bumetanide
ii.   Mercurial agents
·       Mercaptomerin

          3.Acting at distal convoluted tubule
i. Thiazides diuretics - Thiazide diuretics such as hydrochlorothiazide act on the distal convoluted tubule and inhibit the sodium-chloride symporter leading to a retention of water in the urine, as water normally follows penetrating solutes.
· Chlorothiazide, Chlorothalidone, Hydrochlorothiazide, Methyclothiazide, Metolazone
ii.  Sulfonamides
·       Indapemide, Xipemide

           4. Acting at collecting duct system
i.    K- sparing diuretics - These are diuretics which do not promote the secretion of potassium into the urine; thus, potassium is retained and not lost as much as with other diuretics. The term "potassium-sparing" refers to an effect rather than a mechanism or location
      . Aldosterone antagonist - Spironolactone
      . Direct acting - Triamterene, Amiloride
ii.    ADH antagonists
·       Lithium salts, Demeclocycline
               
OTHERS
·    Na/K acetate
·    Na/K bicarbonate
·    Na/K Acetate
·    Albumin
·    Dextrose


ANTI-DIURETICS

An antidiuretic is an agent or drug that, when administered to an organism, helps control body water balance by reducing urination opposing diuresis.Antidiuretics are the drugs that reduce urine volume, particularly in diabetes insipidus (DI) which is their primary indication. 

Classification

1. Antidiuretic hormones - Vasopressin, also known as arginine vasopressin (AVP), antidiuretic hormone (ADH), or argipressin, is aneurohypophysial hormone found in most mammals. Its two primary functions are to retain water in the body and to constrict blood vessels. Vasopressin regulates the body's retention of water by acting to increase water reabsorption in the kidney's collecting ducts, the tubules which receive the very dilute urine produced by the functional unit of the kidney, the nephrons.
  --ADH/Vasopressin, Desmopressin, Lypressin, Terlipressin

2. Miscellaneous
  --Chlorpropamide, Carbamazepine
Sources

Dale, M. M., H. P. Rang, and Maureen M. Dale. 2007. Rang & Dale's pharmacology. [Edinburgh]: Churchill Livingstone.
Laurence L. Brunton (2011). Goodman & Gilman's pharmacological basis of therapeutics. (12th ed.). New York: McGraw-Hill.
http://www.rxlist.com/diuretics/drugs-condition.htm
https://en.wikipedia.org/wiki/Diuretic
https://en.wikipedia.org/wiki/Antidiuretic