Osmotic diuretics
-
These are inert substances filtered into the glomerulus.
-
Their main effect is exerted in the proximal tubule, descending limb of Henle and the collecting duct which are freely permeable to water.
-
By remaining in the tubular lumen, these agents cause an increase in colloid osmotic pressure in the tubular lumen causing suction of water into the tubular lumen.
-
There is also reduced water reabsorption due to renal medullary hyperemia.
-
There is impairment of Na+ reabsorption because the diluted solution in the lumen reduces the Na+ concentration gradient, making it harder for Na+ to be reabsorbed.
-
They are not useful in treating conditions with sodium retention.
-
These drugs are useful in acutely raised intracranial pressure or intraocular pressure.
-
They are also useful in prevention of acute renal failure.
-
Unwanted effects include transient expansion of extracellular fluid volume and hyponatraemia, headache and vomiting.
-
Mannitol is commonly used as an osmotic diuretic and has to be administered intravenously.
-
Isosorbide has the advantage of being absorbed after oral administration in monogastric species.
|
Last modified: Wednesday, 25 April 2012, 12:09 PM