Glycerin
Glycerol (Trihydric alcohol)
Also known as: Osmoglyn · E422 · glicerol · glycerine · glycerolum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acute glaucoma | 1-2 g/kg PO as a 50% oral solution | PO | single dose | — | 🌎 NA |
| Acute glaucoma | 1-2 mL/kg (of a 90% solution) PO | PO | single dose | — | 🌎 NA |
| Acute glaucoma (emergency reduction of IOP) | 1.1-2.2 mL/kg (0.5-1 mL/lb) of 90% syrup | PO | single dose | — | 🌎 NA |
- Acute glaucoma: Withhold water for 3-4 hours after administration.
- Acute glaucoma (emergency reduction of IOP): Mix with an equal volume of ice cream or milk to help reduce vomiting.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acute glaucoma | 1-2 g/kg PO as a 50% oral solution | PO | single dose | — | 🌎 NA |
| Acute glaucoma | 1-2 mL/kg (of a 90% solution) PO | PO | single dose | — | 🌎 NA |
| Acute glaucoma (emergency reduction of IOP) | 1.1-2.2 mL/kg (0.5-1 mL/lb) of 90% syrup | PO | single dose | — | 🌎 NA |
- Acute glaucoma: Withhold water for 3-4 hours after administration.
- Acute glaucoma (emergency reduction of IOP): Mix with an equal volume of ice cream or milk to help reduce vomiting.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Glycerin (also known as glycerol) is a potent, orally administered hyperosmotic agent. In veterinary medicine, it is primarily utilized in emergency settings for the rapid, short-term reduction of intraocular pressure (IOP) in patients suffering from acute glaucoma, and occasionally to reduce cerebrospinal fluid (CSF) pressure.
- Key Advantages: Unlike mannitol, which requires intravenous administration, glycerin can be given orally, making it highly accessible for immediate clinic use during an ocular emergency.
- Clinical Pearl: Because glycerin is metabolized into carbohydrates (glucose) in the liver, it provides a caloric load and can significantly elevate blood glucose levels. Therefore, it is generally contraindicated or used with extreme caution in diabetic patients.
Mechanism of action
Glycerin exerts its effects purely through physical osmotic forces rather than specific receptor interactions.
- Osmotic Gradient: When administered orally, it rapidly increases the osmolality of the blood plasma.
- Fluid Shift: This hyperosmolar state draws water from extravascular spaces (including the aqueous and vitreous humor of the eye, and cerebrospinal fluid) into the intravascular space → Decreased IOP and Decreased CSF pressure.
- Metabolism: Once in the liver, glycerin is metabolized via the enzyme glycerol kinase → glycerol-3-phosphate → enters glycolysis and gluconeogenesis pathways.
Safety & warnings
Contraindications
- Known hypersensitivity to glycerin
- Well-established anuria
- Severe dehydration
- Severe cardiac decompensation
- Frank or impending acute pulmonary edema
- Diabetes mellitus (relative/absolute depending on source)
- Chronic renal failure or compromised renal function
Adverse effects
- Vomiting (most common)
- Headache (reported in humans)
- Nausea
- Thirst
- Diarrhea
Precautions
Use with caution in animals when the blood:ocular barrier is not intact (e.g., hyphema, uveitis), and in those with hypovolemia, cardiac disease, or diabetes. Acute urinary retention should be avoided during the preoperative period. Safety in pregnant animals is unknown (FDA Category C in humans); use only when potential benefits outweigh the risks. Lactation safety is unknown.
Drug interactions
Concomitant administration may prolong the IOP-reducing effects of glycerin.
Concomitant administration may prolong the IOP-reducing effects of glycerin.
Monitoring
- Intraocular pressure (IOP)
- Urine output
- Hydration status
Pharmacokinetics
Absorption
Rapidly absorbed from the GI tract. Decreases in IOP can be seen within 30 minutes; peak serum levels generally occur within 90 minutes. Maximum decreases in IOP usually occur within an hour of dosing and persist for up to 10 hours.
Distribution
Distributed throughout the blood.
Metabolism
Primarily metabolized by the liver.
Elimination
About 10% of the drug is excreted unchanged in the urine.
Overdose
Specific veterinary overdose information is limited. However, cardiac arrhythmias, non-ketotic hyperosmolar coma, and severe dehydration have been reported with the drug. Treatment should be supportive and symptomatic, focusing on restoring fluid and electrolyte balance.
Available products
Formulations
- Oral liquid (50%)
- Oral syrup (90%)
Human-labeled
- Glycerin Oral Liquid: 50% (0.6 g glycerin/mL) in 220 mL; Osmoglyn® (Alcon)
- USP glycerin 90% (can be used for oral use in small animals)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Glycerin oral solution should be stored in tight containers at room temperature; protect from freezing.
Client information
Important: This medication is typically given in the clinic during an eye emergency (like acute glaucoma) to rapidly save your pet's vision.
- Withholding Water: You may be instructed to withhold water from your pet for 3-4 hours after they receive this medication. Why? Drinking water will counteract the drug's ability to pull excess fluid out of the eye.
- Nausea/Vomiting: Glycerin is a very sweet, thick syrup that can upset the stomach. Mixing it with a small amount of milk or ice cream can help prevent vomiting.
- Monitoring: Watch for signs of dehydration or excessive urination once you take your pet home.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.