1. Clinical Overview
A fixed-dose combination of two osmotic agents, Glycerin and Mannitol, primarily used for the management of cerebral edema and reduction of intraocular pressure (IOP). Glycerin is a trihydric alcohol and Mannitol is a hexahydric alcohol. In combination, they exert a synergistic osmotic effect, drawing fluid from tissues into the intravascular compartment, thereby reducing edema and pressure. This combination is particularly relevant in the Indian context for managing acute episodes of raised intracranial pressure (ICP) and acute glaucoma, often as an adjunct to other therapies.
| Onset | Duration | Bioavailability |
|---|---|---|
| Intraocular Pressure (IOP) reduction begins within 10-30 minutes of oral administration. Peak reduction in ICP occurs within 30-60 minutes. | Approximately 4 to 6 hours for IOP reduction. Effects on cerebral edema can last 3 to 8 hours depending on the clinical condition. | Glycerin: Nearly 100% absorbed from the GI tract. Mannitol: Poor oral bioavailability (<20%) due to limited gastrointestinal absorption; it acts primarily as an osmotic laxative when given orally. The combination's systemic osmotic effect is primarily driven by absorbed Glycerin. |
2. Mechanism of Action
The combination creates a hyperosmotic state. After absorption, Glycerin increases plasma osmolality, drawing water from extravascular spaces (including the brain and eye) into the intravascular compartment. This reduces brain volume and intracranial pressure (ICP) and lowers intraocular fluid volume, decreasing IOP. Mannitol, when absorbed in minimal amounts, contributes to this effect. Orally, unabsorbed Mannitol exerts an osmotic effect in the gastrointestinal lumen, acting as a laxative, which may indirectly help in reducing straining-induced ICP spikes.
3. Indications & Uses
- Reduction of raised intracranial pressure (ICP) associated with cerebral edema (e.g., post-traumatic, post-operative)
- Management of acute angle-closure glaucoma (to lower intraocular pressure as an interim measure before definitive therapy)
4. Dosage & Administration
Adult Dosage: 1 to 2 tablets orally, every 6 to 8 hours, as directed by the physician. The dose must be individualized based on the osmolality gap and clinical response. Maximum daily dose should not exceed 6 tablets (60mg Glycerin + 60mg Mannitol) without close monitoring.
Administration: Administer orally with a full glass of water. Can be taken with or without food, but taking on an empty stomach may provide a slightly faster onset. The tablet should be swallowed whole. Patient should be adequately hydrated unless contraindicated.
5. Side Effects
Common side effects may include:
- Headache (rebound), Nausea, Thirst, Dry mouth
- Mild diarrhea or loose stools (due to osmotic effect of unabsorbed Mannitol)
- Dizziness, lightheadedness
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Diuretics (Furosemide, HCTZ) | Additive risk of dehydration and electrolyte depletion (hypokalemia, hyponatremia). | Major |
| Lithium | Mannitol may increase renal excretion of lithium, reducing its serum levels and efficacy. | Moderate |
| Nephrotoxic drugs (Aminoglycosides, NSAIDs, Cisplatin) | Increased risk of acute kidney injury. Mannitol may potentiate nephrotoxicity. | Major |
| Cardiac Glycosides (Digoxin) | Hypokalemia induced by this combination can precipitate digoxin toxicity. | Major |
| Antihypertensives | Additive hypotensive effect due to volume depletion. | Moderate |
7. Patient Counselling
- DO take exactly as prescribed by your doctor.
- DO drink adequate water unless your doctor has advised fluid restriction.
- DO monitor your weight daily if on prolonged therapy and report sudden changes.
- DONT take if you are not producing urine.
- DONT use salt substitutes or take potassium supplements without consulting your doctor.
- DONT drive or operate heavy machinery if you feel dizzy or have blurred vision.
8. Toxicology & Storage
Overdose: Symptoms of overdose include severe dehydration, hypernatremia, hypokalemia, metabolic acidosis, hypotension, shock, acute renal failure, pulmonary edema, confusion, seizures, and coma. GI symptoms include severe diarrhea, nausea, and vomiting.
Storage: Store in a cool, dry place, protected from light and moisture. Keep the container tightly closed. Do not store in the bathroom. Keep out of reach of children. Store at a temperature not exceeding 30°C. Do not use after the expiry date printed on the pack.