Glycerin

Glycerin, or glycerol, is a small polyol used for different osmotic effects according to the route and formulation. Oral glycerin has been used for temporary reduction of intraocular pressure in small animals with acute glaucoma. Rectal preparations have a separate role as stool-softening or evacuation aids. Veterinary use is less common than that of several alternative agents.

Group

Osmotic agent

Mechanism of Action

After oral absorption, glycerol can increase plasma osmolality and create a gradient that draws water from ocular tissues into the circulation, reducing vitreous volume and potentially lowering intraocular pressure. The magnitude of this effect is variable. In rectal preparations, local hygroscopic and osmotic effects increase water in the fecal mass and promote evacuation, with lubrication contributing to easier stool passage.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Osmotic treatment	Reference only	PO		1–2 mL/kg every 8 hours. The source does not tie this volume to a clear concentration; do not calculate a mass dose from the separate emulsion description.
Acute glaucoma	1–2 g/kg	PO		Do not use in: Anuria, Severe dehydration, Severe cardiac decompensation, Acute pulmonary edema; Use an appropriate oral glycerin solution; reassess intraocular pressure, hydration and urine output.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Osmotic treatment	Reference only	PO		1–2 mL/kg every 8 hours. The source does not tie this volume to a clear concentration; do not calculate a mass dose from the separate emulsion description.
Acute glaucoma	1–2 g/kg	PO		Do not use in: Anuria, Severe dehydration, Severe cardiac decompensation, Acute pulmonary edema; Use an appropriate oral glycerin solution; reassess intraocular pressure, hydration and urine output.

Indications

Short-term osmotic reduction of intraocular pressure in selected dogs with acute glaucoma, with variable response and limited comparative evidence.
Rectal softening or evacuation of hard feces in selected constipated veterinary patients using an appropriate preparation.

Contraindications

Dehydration

Adverse effects

Fluid and electrolyte depletion

Preparations

Preparation	Form	Strength	Route
Osmoglyn oral glycerin 0.6 g/mL The supplied source explicitly equates this 50% oral product to 0.6 g glycerin/mL; this is not a general conversion for every percentage-labelled glycerin solution.	Oral Liquid	0.6 g / mL	PO

Monitoring and Administration

Monitor intraocular pressure, hydration and electrolytes. Other agents are more commonly used for acute glaucoma.