• Introduction:

  •  Osmotic diuretics cause water to be retained within the proximal tubule and descending limb of loop of Henle (freely permeable to water)

  •  Mannitol is an example of osmotic diuretic.

  •  Clinical Use: mainly used to reduce increased intracranial pressure;

• Osmotic diuretics: properties

  • Mannitol: not metabolized, freely filtered at the glomerular

  • Usually administered by IV; oral administration results in an osmotic diarrhea-- perhaps useful to promote elimination of toxic substances from the GI tract (in conjunction with activated charcoal)

  • Urine volume increases with mannitol excretion due to direct osmotic effects

    •  Sodium reabsorption is reduced because of increased urine flow rates {decreased contact time between urine and tubular epithelial cells}

• Clinical Uses:

  • To decrease intracranial or intraocular pressure:

    •  Mannitol extract water from intracellular compartments, reducing total body water

    •  Following IV administration, intracranial pressure falls within 60-90 minutes.

  •  To increase urine volume:

    • May be used to prevent anuria if the kidney due to hemolysis or rhabdomyolysis is presented with a large pigmented load.

    • When renal hemodynamics are compromised

•  Toxicity:

  • Volume expansion effects -- increased extra cellular fluid volume and hyponatremia may cause pulmonary edema, complicating congestive heart failure

  • Headache, nausea, vomiting -- commonly observed

  • Dehydration and hypernatremia:

    •  fluid loss leads to significant dehydration and in the absence of adequate fluid replacement leads to hypernatremia.

Ives, H.E., Diuretic Agents, in: Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 242-259.