Glycerin

Usage

• Medical Conditions: Glycerin is used for treating constipation, reducing intraocular pressure (IOP) before eye surgery or in glaucoma, reducing brain edema associated with conditions like stroke, meningitis, or CNS tumors, and facilitating passage of meconium in newborns. It is also used as a moisturizer for the skin.
• Pharmacological Classification: Osmotic laxative (rectal), osmotic diuretic (oral), ophthalmic osmotic agent.
• Mechanism of Action: Glycerin works by drawing water into the colon (rectal use), increasing plasma osmolality (oral use), or drawing fluid out of the cornea (ophthalmic use).

Alternate Names

• Glycerol
• Glycerine
• Osmoglyn (brand name)
• Ophthalgan (brand name)

How It Works

• Pharmacodynamics: Orally or intravenously, glycerin elevates blood plasma osmolality, creating an osmotic gradient that draws water from tissues into the vascular space. Rectally, it softens stool and stimulates bowel movements. In the eye, it dehydrates the cornea, reducing IOP.
• Pharmacokinetics: Glycerin is readily absorbed from the gastrointestinal tract. It is metabolized primarily in the liver and eliminated by the kidneys.
• Mode of Action: Glycerin exerts its effects through osmotic action. It does not bind to receptors, inhibit enzymes, or modulate neurotransmitters.
• Elimination Pathways: Primarily renal excretion; hepatic metabolism plays a lesser role.

Dosage

Standard Dosage

Adults:

• Constipation (rectal): 2-3 g suppository once daily or 5-15 mL enema once daily.
• IOP reduction (oral): 1-2 g/kg one time, 1-1.5 hours before surgery.
• Cerebral edema (oral/IV): 0.5 to 2 g/kg every 4 to 6 hours.
• Cough (oral): 5-10 mL of a 15% v/v syrup 3-4 times daily.

Children:

• Constipation (rectal): 1-1.7 g suppository (ages 2-6), or 2-2.1g suppository (ages 6 and above) once daily; or 2-5 mL enema (ages 2-6), or 5-15 ml enema (ages 6 and above) once daily.
• IOP reduction (oral): 1-1.5 g/kg one time.
• Cough (oral): 5 mL of a 15% v/v syrup 3-4 times daily (ages 3 months to 5 years).
• Meconium passage (rectal): 0.2 mL of diluted 80% glycerol solution (neonates).
• Pediatric Safety Considerations: Adjust doses based on body weight. Rectal glycerin is generally safe for children.

Special Cases:

• Elderly Patients: Start at lower doses due to potential for age-related decline in renal function.
• Patients with Renal Impairment: Dose adjustment may be necessary based on creatinine clearance.
• Patients with Hepatic Dysfunction: Use cautiously, as the liver plays a role in glycerol metabolism.
• Patients with Comorbid Conditions: Consider individual patient characteristics and comorbidities like diabetes, cardiovascular disease, dehydration, and hypervolemia.

Clinical Use Cases

• Intubation: Nitroglycerin, not glycerin, is used in some protocols to attenuate the hemodynamic response to intubation (not glycerol). 0.4 mg (1 spray) to 0.8 mg (2 sprays) one minute before intubation may be administered.
• Surgical Procedures: Glycerin can be used preoperatively to reduce IOP before eye surgeries and brain volume before neurosurgical procedures.
• Mechanical Ventilation: Not typically used with glycerol.
• Intensive Care Unit (ICU) Use: Intravenous glycerin may be used for cerebral edema management under close monitoring.
• Emergency Situations: May be used in the emergency department for cerebral edema and acute glaucoma.

Dosage Adjustments

Adjustments required in renal/hepatic dysfunction, dehydration, and hypervolemia.

Side Effects

Common Side Effects

• Headache
• Dizziness
• Nausea
• Vomiting
• Thirst
• Diarrhea
• Bloating
• Rectal irritation (with suppositories)

Rare but Serious Side Effects

• Cardiac arrhythmias
• Severe dehydration
• Hyperglycemia

Long-Term Effects

Laxative dependence with chronic use.

Adverse Drug Reactions (ADR)

Hypersensitivity reaction, severe dehydration, hyperosmolar syndrome, hemolysis (with rapid IV infusion).

Contraindications

• Hypersensitivity to glycerin
• Diabetic ketoacidosis
• Anuria
• Severe dehydration
• Intestinal obstruction or perforation
• Rectal bleeding

Drug Interactions

No significant known drug interactions with glycerin.

Pregnancy and Breastfeeding

Limited information. Generally considered safe for short-term use. Consult with a physician to assess potential risks and benefits.

Drug Profile Summary

• Mechanism of Action: Osmotic action.
• Side Effects: Headache, dizziness, nausea, vomiting, thirst, diarrhea.
• Contraindications: Hypersensitivity, anuria, intestinal obstruction, rectal bleeding.
• Drug Interactions: None known.
• Pregnancy & Breastfeeding: Limited data, generally considered safe for short-term use.
• Dosage: Variable, depending on indication and patient factors. See dosing section.
• Monitoring Parameters: Fluid balance, electrolytes, renal function (with high doses), IOP (ophthalmic use).

Popular Combinations

Glycerin is not typically used in fixed combinations with other drugs.

Precautions

• General Precautions: Assess for contraindications, dehydration, electrolyte imbalances.
• Specific Populations: Use cautiously in pregnancy/breastfeeding, children, elderly, and patients with renal/hepatic dysfunction.
• Lifestyle Considerations: Adequate hydration is important, especially with oral or IV use.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Glycerin?

A: The dosage varies depending on the indication, route of administration, and patient factors. Refer to the detailed dosage guidelines provided above.

Q2: How should glycerin be administered for constipation?

A: Rectally, as a suppository or enema. The typical adult dose is 2-3 g suppository or 5-15 mL enema once as needed.

Q3: Can glycerin be used in pregnant women?

A: Consult with a doctor. Glycerin is generally considered safe for short-term use during pregnancy, but data are limited.

Q4: What are the common side effects of oral glycerin?

A: Headache, dizziness, nausea, vomiting, thirst, and diarrhea.

Q5: What are the contraindications to using glycerin?

A: Hypersensitivity to glycerin, anuria, severe dehydration, intestinal obstruction, rectal bleeding, and diabetic ketoacidosis.

Q6: How does glycerin reduce IOP?

A: By increasing plasma osmolality, which draws fluid from the eye into the vascular space.

Q7: Is glycerin safe for long-term use as a laxative?

A: Chronic use can lead to dependence. It is advisable to address the underlying cause of constipation and use glycerin only intermittently.

Q8: How should glycerin be administered for cerebral edema?

A: Orally or intravenously, under the guidance of a healthcare professional. Dosing is typically 0.5 to 2g/kg body weight every 4 to 6 hours.

Q9: What are the potential drug interactions with glycerin?

A: Glycerin has no known significant drug interactions.

Q10: Can glycerin be used in newborns?

A: Yes, a small sliver of a glycerin suppository or a small amount of diluted liquid glycerol can be administered rectally to facilitate meconium passage. Consult local guidelines for specific recommendations for neonates.