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Osmotic Diuretics
  • 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.


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