Description
Uses and Administration
Glycerol is an osmotic dehydrating agent with hygroscopic and lubricating properties. When given orally or parenterally, glycerol increases the plasma osmolality, resulting in the movement of water by osmosis from the extravascular spaces into the plasma.
Glycerol is given by mouth for the short-term reduction of vitreous volume and intra-ocular pressure before and after ophthalmic surgery, and as an adjunct in the management of acute glaucoma. Its onset of action is rapid, with a maximal reduction in intra-ocular pressure occurring about 1 to 11/2 hours after a dose; the duration of action is about 5 hours. The usual initial dose of glycerol is 1 to 1.8 g/kg given as a 50% solution. There can be problems of palatability when glycerol solutions are given orally; chilling or flavouring the solutions may help.
Glycerol may be applied topically to reduce corneal oedema, but as the effect is only transient its use is primarily limited to facilitating ocular examination and diagnosis. Glycerol eye drops can be painful on instillation and the prior application of a local anaesthetic has been recommended.
Glycerol has also been given by mouth or intravenously to reduce intracranial pressure.
Glycerol may be used rectally as suppositories or a solution in single doses to promote faecal evacuation in the management of constipation. It usually acts within 15 to 30 minutes. Glycerol is commonly classified as an osmotic laxative but may act additionally or alternatively through its local irritant effects; it may also have lubricating and faecal softening actions.
Glycerol is used as a demulcent in cough preparations.
Glycerol has a wide range of applications in pharmaceutical formulation; these include its use as a vehicle and solvent, as a sweetening agent, as a preservative in some liquid medications, as a plasticiser in tablet film-coating, and as a tonicity adjuster. It is often included in topical preparations such as eye drops, creams, and lotions as a lubricant and also for its moisturising properties since, when absorbed, its hygroscopic action may enhance moisture retention. Ear drops for the removal of ear wax often contain glycerol as a lubricating and softening agent.
Glycerol is also used as a cryoprotectant in cryopreservation.
Adverse Effects and Precautions
The adverse effects of glycerol are primarily due to its dehydrating action.
When taken by mouth glycerol may cause headache, nausea, and vomiting; diarrhoea, thirst, dizziness, and mental confusion may occur less frequently. Cardiac arrhythmias have been reported.
Glycerol increases plasma osmolality resulting in the withdrawal of water from the extravascular spaces. The consequent expansion of extracellular fluid, especially if sudden, can lead to circulatory overload, pulmonary oedema, and heart failure; glycerol must therefore be used with caution in patients at risk, such as those with hypervolaemia, cardiac failure, or renal disease. Severe dehydration can occur and glycerol should be used cautiously in dehydrated patients. Patients with diabetes mellitus may additionally develop hyperglycaemia and glycosuria following metabolism of glycerol. Nonketotic hyperosmolar hyperglycaemic coma is rare, but fatalities have been reported.
Haemolysis, haemoglobinuria, and acute renal failure have also been associated with glycerol when given intravenously.
Glycerol can cause irritation when given topically or rectally. A local anaesthetic may be used before application of glycerol to the cornea to reduce the likelihood of a painful response.
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