Osmotic diuretics
The term osmotic diuretic applies to compounds which are freely filtered by the glomerulus, are not reabsorbed by the renal tubule, are generally inert from a pharmacological point of view and can thus be given in large quantity.
At the level of the proximal tubule, there is an active reabsorption of salts and a passive reabsorption of water to keep an iso-osmotic equilibrium with that of the plasma. The presence of a high concentration of an osmotic diuretic in the lumen of the nephron increases the osmolality and decreases the reabsorption of water and electrolytes.
The osmotic compounds used as diuretics are mannitol and glycerol.
Mannitol is given by intravenous infusion at the concentration of 10 to 25% because it is not absorbed by the digestive tract. When the volume infused is important, there may be risk of increase in plasma volume.
Glycerol can be administered by intravenous infusion and oral route with a good bioavailability.
Mannitol and glycerol have two therapeutic uses:
- the decrease of intracranial pressure and cerebral liquid mass before neurosurgical intervention.
- the decrease of intraocular pressure for the treatment of glaucoma or surgical operation on the eye.
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