What are the uses and dosing of mannitol (osmotic diuretic) injection?

Uses and Dosing of Mannitol (Osmotic Diuretic) Injection

Mannitol injection is primarily indicated for the reduction of intracranial pressure and brain mass, reduction of high intraocular pressure, and measurement of glomerular filtration rate. 1

Therapeutic Indications

Reduction of Intracranial Pressure (ICP)

• Recommended for treating threatened intracranial hypertension or signs of brain herniation after controlling secondary brain insults 2
• Effectively reduces pathological ICP, with reduction proportional to the degree of intracranial hypertension 3
• Maximum effect observed after 10-15 minutes with effects lasting 2-4 hours 4
• Among therapies that decrease ICP (mannitol, external ventricular drainage, and hyperventilation), mannitol is the only one associated with improved cerebral oxygenation 2

Reduction of High Intraocular Pressure

• FDA-approved indication for reducing elevated intraocular pressure 1

Diagnostic Use

• Measurement of glomerular filtration rate 1

Dosing Guidelines

For Intracranial Hypertension

• FDA recommendation: 0.25 to 2 g/kg body weight as a 15% to 25% solution administered over 30-60 minutes 1
• American Heart Association recommendation: 0.25 to 0.5 g/kg IV administered over 20 minutes, which can be given every 6 hours 4
• For traumatic brain injury: 250 mOsm dose (approximately 20% mannitol) infused over 15-20 minutes 2
• For small or debilitated patients: 500 mg/kg 1
• Maximum daily dose: 2 g/kg to avoid potential adverse effects 4

For Pediatric Patients

• 1 to 2 g/kg body weight or 30 to 60 g/m² body surface area over 30-60 minutes 1

For Glomerular Filtration Rate Measurement

• 100 mL of a 20% solution (20 g) diluted with 180 mL of sodium chloride injection, or 200 mL of a 10% solution (20 g) diluted with 80 mL of sodium chloride injection 1
• The resulting 280 mL of 7.2% solution is infused at a rate of 20 mL per minute 1

Monitoring Parameters

Efficacy Monitoring

• ICP reduction is typically maximal 40 minutes after start of infusion and can last up to 100 minutes 5
• Smaller and more frequent doses may be as effective in reducing ICP while avoiding risks of osmotic disequilibrium and severe dehydration 6

Safety Monitoring

• Serum osmolality should be monitored to ensure it remains below 320 mOsm/L 4, 7
• Discontinue mannitol when:
  • Serum osmolality exceeds 320 mOsm/L 7
  • After 2-4 doses (maximum 2 g/kg total) 7
  • No clinical improvement in neurological status despite treatment 7
  • Renal, cardiac, or pulmonary status worsens 1

Contraindications

• Well-established anuria due to severe renal disease 1
• Severe pulmonary congestion or frank pulmonary edema 1
• Active intracranial bleeding except during craniotomy 1
• Severe dehydration 1
• Progressive heart failure or pulmonary congestion after institution of mannitol therapy 1
• Known hypersensitivity to mannitol 1

Important Clinical Considerations

• Mannitol is often used as a temporizing measure before patients undergo definitive treatment such as decompressive craniectomy 4
• At equiosmotic dose (about 250 mOsm), mannitol and hypertonic saline have comparable efficacy in treating intracranial hypertension 2
• Prophylactic administration of mannitol is not recommended in patients without evidence of increased ICP 7
• Side effects include osmotic diuresis requiring volume compensation 2
• Monitoring fluid, sodium, and chloride balances is necessary during mannitol therapy 2
• Despite intensive medical management with mannitol, mortality in patients with increased ICP remains high (50-70%) 4

Potential Adverse Effects

• Fluid and electrolyte imbalances (hypernatremia, hyponatremia) 1
• Renal complications including renal failure, especially with pre-existing renal disease 1
• Central nervous system toxicity: may increase cerebral blood flow and risk of postoperative bleeding in neurosurgical patients 1
• Pulmonary congestion, acidosis, electrolyte loss, dryness of mouth, thirst, marked diuresis, urinary retention 1