Oral Glycerol: Clinical Uses and Dosing
Oral glycerol is primarily used as an osmotic agent to reduce intracranial pressure and intraocular pressure, with typical dosing of 0.5-2.0 g/kg administered intermittently rather than continuously to avoid rebound cerebral overhydration. 1, 2
Primary Clinical Indications
Oral glycerol functions as a potent osmotic dehydrating agent with additional effects on brain metabolism, effective for:
- Elevated intracranial pressure in multiple conditions including Reye's syndrome, stroke, encephalitis, meningitis, pseudotumor cerebri, CNS tumors, and space-occupying lesions 1
- Intraocular pressure reduction in glaucoma 1, 3
- Postural syncope and improved rehydration during acute gastrointestinal disease 3
Dosing Protocols
Standard Dosing for Intracranial Hypertension
- Dose range: 0.5-1.0 g/kg orally 2
- Alternative range: 0.25-2.0 g/kg depending on severity 1
- Administration frequency: Intermittent dosing is preferred over continuous administration to minimize rebound cerebral overhydration 1
Pharmacokinetic Considerations
- Absorption: Rapid intestinal absorption with peak serum levels occurring 1-2 hours after ingestion 4
- Peak concentrations: 1285-2238 mg/L (median 1770 mg/L) after 1.2 g/kg dose 4
- Elimination half-life: 0.61-1.18 hours 4
- Osmolality effect: Doses >1.0 g/kg increase serum osmolality by >10 mOsmol/kg 3, 4
Safety Profile and Monitoring
Advantages of Oral Administration
- No hemolysis risk with oral use (unlike IV administration) 1
- Metabolized in liver, reducing systemic dehydration compared to other osmotic agents 2
- Minimal electrolyte disturbances with only minor changes in serum electrolytes, glucose, and urea nitrogen 2
Expected Osmolality Changes
- Baseline serum osmolarity: ~305 mOsm/L 2
- After 10 days of therapy: ~355 mOsm/L 2
- Resting serum glycerol: ~0.05 mmol/L, increasing to ~20 mmol/L after doses >1.0 g/kg 3
Critical Monitoring Parameters
For severe elevated ICP requiring higher doses (1-2 g/kg every 2 hours):
- Glycerol serum concentration monitoring required 1
- Serum osmolality monitoring required 1
- ICP monitoring to optimize therapy 1
Important Clinical Caveats
Rebound cerebral overhydration is the primary concern, especially in patients with altered blood-brain barriers—this can be avoided by using intermittent rather than continuous dosing schedules 1. The medication has been used safely in clinical practice for decades (widespread use 1961-1980) with an established safety profile 3.
Glycerol Hyperhydration (Alternative Use)
Since 1987, glycerol ingestion with added fluid has been used to increase total body water by up to 700 mL, providing benefits for thermoregulation and endurance during exercise or heat exposure, though this represents a distinct application from its osmotic therapeutic use 3.
Note on Constipation Management
While the question asks about oral glycerol, it's important to distinguish this from glycerin (glycerol) suppositories used for constipation. For fecal impaction, glycerin suppositories may be administered rectally 5, but oral glycerol is not indicated for constipation management. For oral osmotic laxative therapy, polyethylene glycol (PEG) is the preferred agent 6.