Pharm 101: Mannitol


Osmotic diuretic

  • Osmotic diuretic
  • Renal:
    • Acts on PCT and descending limb of loop of Henle
    • Opposes the action of ADH in collecting tubules
  • CNS:
    • Alters Starling forces as it does not cross intact blood-brain barrier
    • Draws water out of cells and reduces intracellular volume, which reduces intracranial volume and ICP

  • Poor absorption (oral administration causes osmotic diarrhoea rather than diuresis)
  • Not metabolised
  • Excreted by glomerular filtration in 30-60 minutes

Clinical uses
  • Reduction of intracranial pressure in intracranial haemorrhage:
    • 1-2g/kg as IV bolus over 15 minutes
    • ICP should fall within 60-90 minutes
  • Reduction of IOP before ophthalmologic procedures
  • Controversial, for diuresis in haemolysis or rhabdomyolysis

Adverse effects
  • Extracellular volume expansion
    • Flash APO
    • Relative hyponatraemia prior to diuresis
    • Headache, nausea and vomiting
  • Dehydration, hyperkalaemia, hypernatraemia
  • Hyponatraemia in renal failure (mannitol cannot be excreted)
  • AKI in 6-7%

  • Renal failure
  • CCF due to risk of APO

Further Reading

Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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