Pharm 101: Mannitol

Class

Osmotic diuretic

Pharmacodynamics

• 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

Pharmacokinetics

• 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%

Precautions/contraindications

• Renal failure
• CCF due to risk of APO

Further Reading

• Nickson C. Traumatic Brain Injury (TBI) Management
• Nickson C. Subarachnoid Haemorrhage: Initial Management