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Mannitol osmolarity effects


  • Mannitol is an Osmotic diuretic
  • 6 carbon sugar
  • Dose: 0.25-1.0 g/kg
  • Filtered at the glomerulus, but does not get significant reabsorption in the proximal tubule. This osmotically prevents passive water reabsorption that would occur with the active Na+ reabsorption in the proximal tubule
  • Rapidly acting, therefore this acutely raises plasma/extracellular osmolarity
  • Leads to hyperosmolality, hyponatremia, hypokalemia.


  • Prophylaxis against ARF in high risk patients (rhabdomyolysis, massive trauma, hemolytic reactions, severe jaundice, cardiac/major vascular surgery)
  • Transplant surgery
  • Acute reduction of intraocular pressure
  • Acute reduction of intracranial pressure/cerebral edema
  • Forced diuresis to remove toxic substances (acute drug overdose)


  • Causes a transient and rapid intracellular to extracellular water shift
  • This can cause fluid overload leading to CHF and pulmonary edema
  • Transient hyponatremia
  • Mild/moderate transient increase in plasma potassium
  • Be careful giving large boluses too rapidly. May be advisable to give large bolus in divided doses over ½ hour or longer