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
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Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Co-creator of the LITFL ECG Library. Twitter: @rob_buttner