Introduction
Glycerin (also known as glycerol) is a simple polyol compound with multiple pharmaceutical applications. As a trihydric alcohol, it serves as an osmotic agent, humectant, solvent, and lubricant in various medicinal formulations. First isolated in 1779 by Swedish chemist Carl Wilhelm Scheele, glycerin has become an essential component in numerous pharmaceutical, cosmetic, and food products due to its versatile properties and favorable safety profile.
Mechanism of Action
Glycerin exerts its therapeutic effects primarily through its osmotic properties. When administered orally or rectally, glycerin draws water into the intestinal lumen through osmosis, increasing stool water content and promoting peristalsis. As an ophthalmic agent, it creates an osmotic gradient that draws fluid from the corneal stroma, reducing corneal edema. In neurological applications, intravenous glycerin reduces brain volume by creating an osmotic gradient that draws fluid from the brain into the vascular compartment.
Indications
- Constipation: As a hyperosmotic laxative for relief of occasional constipation
- Ophthalmic edema: Reduction of corneal edema during ophthalmic examinations
- Increased intracranial pressure: Management of elevated intracranial or intraocular pressure (off-label)
- Topical applications: As a humectant in dermatological preparations for dry skin conditions
- Excipient: As a solvent, preservative, and sweetening agent in various pharmaceutical formulations
Dosage and Administration
Oral (laxative):- Adults: 2-6 g (5-15 mL) as a single dose
- Children ≥6 years: 2-4 g (5-10 mL) as a single dose
- Administer with a full glass of water
- Adults: 1 suppository (2-3 g) inserted rectally as needed
- Children: 1 pediatric suppository (1-1.5 g) as needed
- 1-2 drops of sterile ophthalmic solution applied topically to the eye as needed
- Renal impairment: Use with caution; monitor fluid and electrolyte balance
- Hepatic impairment: No specific dosage adjustments required
- Elderly: Consider reduced dosage due to increased sensitivity to osmotic effects
- Pregnancy: Category C; use only if clearly needed
- Lactation: Compatible with breastfeeding
Pharmacokinetics
Absorption: Orally administered glycerin is rapidly absorbed from the gastrointestinal tract (approximately 80% bioavailability). Rectal administration results in minimal systemic absorption. Distribution: Widely distributed throughout body water with minimal protein binding. Metabolism: Primarily metabolized in the liver via glycolysis and gluconeogenesis pathways. Approximately 10-20% is converted to glucose and glycogen. Elimination: Renal excretion of unchanged drug is minimal (<10%). The majority is metabolized to carbon dioxide and water via normal metabolic pathways. Half-life is approximately 30-45 minutes.Contraindications
- Hypersensitivity to glycerin or any component of the formulation
- Acute abdominal conditions including appendicitis, intestinal obstruction, or acute surgical abdomen
- Severe dehydration
- Anuria or severe renal impairment
- Diabetic ketoacidosis
Warnings and Precautions
- May cause excessive bowel activity and dehydration with prolonged use
- Use with caution in patients with cardiac disease due to potential fluid shifts
- Monitor diabetic patients for hyperglycemia as glycerin can be metabolized to glucose
- Rectal administration may cause local irritation or burning sensation
- Avoid use in patients with nausea, vomiting, or abdominal pain until etiology determined
- Prolonged ophthalmic use may cause irritation and rebound hyperemia
Drug Interactions
- Diuretics: Enhanced risk of dehydration and electrolyte disturbances
- Corticosteroids: May potentiate hyperglycemic effects
- Other laxatives: Increased risk of excessive bowel activity and dehydration
- Lithium: Altered renal clearance potentially affecting lithium levels
- Antihypertensive medications: Potential enhanced hypotensive effects due to fluid shifts
Adverse Effects
Common:- Gastrointestinal: Nausea, diarrhea, abdominal cramping, flatulence
- Rectal: Burning sensation, irritation
- Ophthalmic: Transient stinging, blurred vision
- Severe dehydration and electrolyte imbalances
- Hypersensitivity reactions
- Cardiac arrhythmias secondary to electrolyte disturbances
- Severe headache or confusion from rapid fluid shifts
Monitoring Parameters
- Bowel function and stool consistency
- Hydration status (skin turgor, mucous membranes, urine output)
- Electrolyte levels with prolonged use (especially potassium, sodium)
- Blood glucose in diabetic patients
- Neurological status when used for intracranial pressure reduction
- Ophthalmological examinations with prolonged ophthalmic use
Patient Education
- Take oral preparation with plenty of water to enhance effectiveness and prevent dehydration
- Do not use for more than 7 days without consulting healthcare provider
- Report severe abdominal pain, rectal bleeding, or no bowel movement after use
- Diabetic patients should monitor blood glucose levels more frequently
- Discontinue use and contact provider if rash, dizziness, or severe cramping occurs
- Store at room temperature away from moisture and heat
- Keep out of reach of children
References
1. American Society of Health-System Pharmacists. AHFS Drug Information. Glycerin monograph. 2023. 2. Lexicomp Online. Glycerin drug monograph. Wolters Kluwer Clinical Solutions. 3. Micromedex Solutions. Glycerin detailed information. IBM Watson Health. 4. National Center for Biotechnology Information. PubChem Compound Summary for CID 753, Glycerol. 5. Sweetman SC, ed. Martindale: The Complete Drug Reference. 38th ed. Pharmaceutical Press; 2014. 6. FDA Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. 7. Clinical Pharmacology [database online]. Tampa, FL: Elsevier; 2023.