glycerin (glycerol)
Fleet Babylax, Ophthalgan, Osmoglyn, Sani-Supp

Available forms
Available by prescription only
Ophthalmic solution: 7.5-ml containers
Oral solution: 50% (0.6 g/ml), 75% (0.94 g/ml)

Available without a prescription
Rectal solution: 4 ml/applicator
Suppository: 1.5 g (infants), 3 g (adults)

Indications and dosages
 Constipation. Adults and children age 6 and older: 3 g as a suppository or 5 to 15 ml as an enema.
Children younger than age 6: 1 to 1.5 g as a suppository or 2 to 5 ml as an enema.
 Reduction of intraocular pressure. Adults: 1 to 2 g/kg P.O. 60 to 90 minutes preoperatively.
 Reduction of corneal edema. Adults: 1 to 2 drops of ophthalmic solution topically before eye examination; 1 to 2 drops q 3 to 4 hours for corneal edema.
 To act as an osmotic diuretic. Adults: 1 to 2 g/kg P.O. 1 to 1 1/2 hours before surgery.

Pharmacodynamics
Laxative action: Glycerin suppositories produce laxative action by causing rectal distention, thereby stimulating the urge to defecate; by causing local rectal irritation; and by triggering a hyperosmolar mechanism that draws water into the colon.
Antiglaucoma action: Orally administered glycerin helps reduce intraocular pressure by increasing plasma osmotic pressure, thereby drawing water into the blood from extravascular spaces. It also reduces intraocular fluid volume independently of routine flow mechanisms, decreasing intraocular pressure; it may cause tissue dehydration and decreased CSF pressure.
Topically applied glycerin produces a hygroscopic (moisture-retaining) effect that reduces edema and improves visualization in ophthalmoscopy or gonioscopy. Glycerin reduces fluid in the cornea via its osmotic action and clears corneal haze.

Pharmacokinetics
Absorption: Rectal form
Absorption: Absorbed poorly; after rectal administration, laxative effect occurs in 15 to 30 minutes.
Distribution: Distributed locally.
Metabolism: No information available.
Excretion: Excreted in feces.
Oral form
Absorption: Absorbed rapidly from GI tract, with serum levels peaking in 60 to 90 minutes with oral administration; intraocular pressure decreases in 10 to 30 minutes. Action peaks in 30 minutes to 2 hours, with effects persisting for 4 to 8 hours. Intracranial pressure (ICP) decreases in 10 to 60 minutes; effect persists for 2 to 3 hours.
Distribution: Distributed throughout blood but doesn’t enter ocular fluid; drug may enter breast milk.
Metabolism: About 80% metabolized in liver, 10% to 20% in kidneys.
Excretion: Excreted in feces and urine.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug. Rectal administration of drug is contraindicated in those with intestinal obstruction. Also contraindicated in patients with anuria, severe dehydration, frank or impending acute pulmonary edema, severe cardiac decompensation, undiagnosed abdominal pain, vomiting, or other signs of appendicitis, fecal impaction, or acute surgical abdomen.
  Use oral form cautiously in elderly or dehydrated patients and in those with hypervolemia, confused mental states, congestive heart disease, diabetes or cardiac, renal, or hepatic disease.

Interactions
Drug-drug. Diuretics: May cause additive effects. Avoid use together.

Adverse reactions
CNS: mild headache, dizziness (with oral administration).
EENT: eye pain, irritation.
GI: cramping pain, thirst, nausea, vomiting, diarrhea (with oral administration); rectal discomfort, hyperemia of rectal mucosa (with rectal administration).
Metabolic: mild hyperglycemia, mild glycosuria.

Effects on lab test results
• May increase glucose levels.

Overdose and treatment
No information available.

Special considerations
• Drug is useful in acute angle-closure glaucoma; before iridectomy (with carbonic anhydrase inhibitors or topical miotics); in trauma or disease, such as congenital glaucoma and some secondary glaucoma forms; and before or after surgery, such as retinal detachment surgery, cataract extraction, or keratoplasty.
• Drug is used to facilitate ophthalmoscopic and gonioscopic examination and to differentiate superficial edema and deep corneal edema.
 ALERT Stop drug if hypersensitivity symptoms occur.
• When administering glycerin orally, don’t give hypotonic fluids to relieve thirst and headache from glycerin-induced dehydration; these will counteract osmotic effects.
• Use topical tetracaine hydrochloride or proparacaine before ophthalmic instillation to prevent discomfort.
• Don’t touch tip of dropper to eye, surrounding tissues, or tear-film; glycerin will absorb moisture.
• To prevent or relieve headache, have patient remain supine during and after oral administration.
• Commercially available solutions may be poured over ice and sipped through a straw.
• Hyperosmolar laxatives are used most commonly to help laxative-dependent patients reestablish normal bowel habits.
• Other uses include reducing ICP in patients with CVA, meningitis, encephalitis, Reye’s syndrome, or CNS trauma or tumors. Also used for reducing brain volume during neurosurgical procedures through oral administration, I.V. administration, or both.
• If excess glycerin is administered into eye, irrigate conjunctiva with sterile normal saline solution or water. Systemic effects aren’t expected.
Breast-feeding patients
• Safety in breast-feeding women hasn’t been established. Possible risks must be weighed against benefits.
Pediatric patients
• Safety and effectiveness of ophthalmic glycerin solutions in children haven’t been established.
Geriatric patients
• Dehydrated elderly patients may experience seizures and disorientation.

Patient education
• Instruct patient to report severe headache after oral dose.
• Teach correct way to instill drops, and warn patient not to touch eye with dropper.
• Tell patient to lie down during and after administration to prevent or relieve headache.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use