VETINUITY
Why do cats need a higher fomepizole dose?
The canine regimen is not the one tested in cats; the feline protocol that protected cats loads at 125 mg/kg. At that dose cats showed mild sedation and no biochemical toxicity.
● ANSWER
Sourced & dated
What is the fomepizole dose for ethylene glycol poisoning in dogs and cats?
Dogs: fomepizole 20 mg/kg IV, then 15 mg/kg at 12 and 24 hours and 5 mg/kg at 36 hours. Cats: 125 mg/kg IV, then 31.25 mg/kg at 12, 24 and 36 hours, started within 3 hours.
● VETINUITY FOMEPIZOLE DOSE CALCULATOR
Vetinuity fomepizole dose calculator
Fomepizole 5% solution (50 mg/mL). The cat regimen is extra-label and works only when started within 3 hours of ingestion.
● WHAT'S DOCUMENTED
Vetinuity’s fomepizole table: dogs get 20 mg/kg IV, then 15 mg/kg IV at 12 and 24 hours and 5 mg/kg IV at 36 hours; cats need 125 mg/kg IV, then 31.25 mg/kg IV at 12, 24 and 36 hours, and only survive reliably when it starts within 3 hours of ingestion. The Vetinuity fomepizole dose calculator above converts each dose to milligrams and millilitres of the 50 mg/mL solution, with the ethanol fallback and calcium correction beside it. The tables sit in the Vetinuity clinical assistant, built by emergency veterinarian Brian Toncray, DVM.
The clock
| Time after ingestion | Cats | Dogs |
|---|---|---|
| 30 min to 12 h | Drunk-like ataxia, vomiting, PU/PD | Same, sometimes a brief recovery near 12 h |
| From 3 h (cats) or 6 h (dogs) | Calcium oxalate crystalluria possible, a poor sign | Same |
| 12 to 24 h | Oliguric acute kidney failure, then anuria | Kidneys still being injured |
| 36 to 72 h | Oliguric acute kidney failure, then anuria |
Undiluted ethylene glycol has a minimum lethal dose of 1.4 mL/kg in cats and 4.4 to 6.6 mL/kg in dogs. Fomepizole blocks alcohol dehydrogenase, so it only helps while unmetabolized glycol is still circulating.
Ethanol when fomepizole is not on the shelf
- Dogs: 5.5 mL/kg of 20% ethanol IV every 4 hours for 5 treatments, then every 6 hours for 4 more.
- Cats: 5 mL/kg of 20% ethanol diluted in IV fluids as a 6-hour drip for 5 treatments, then over 8 hours for 4 more.
- Either species: 30% ethanol 1.3 mL/kg IV bolus, then 0.42 mL/kg/h CRI for 48 hours, which keeps CNS depression steadier and makes glucose easier to manage.
In the feline study only 1 of 3 cats treated with ethanol at 3 hours survived, against all of the fomepizole-treated cats at the same delay.
Supportive care
Emesis or lavage only helps within 1 to 2 hours, and never in an animal with neurologic signs. Correct metabolic acidosis, monitor glucose every 4 to 6 hours during ethanol therapy, and treat hypocalcemia with 10% calcium gluconate (dogs 50-150 mg/kg, cats 94-140 mg/kg, over 20 to 30 minutes) under continuous ECG, ideally guided by ionized calcium.
More: lily toxicity in cats, grapes and raisins and blocked cat hyperkalemia.
● SOURCES
- 1. Merck Veterinary Manual: Ethylene Glycol Toxicosis in Animals. Etiology; Clinical Findings; Diagnosis; Treatment. Checked 2026-10-26.
- 2. Connally HE, Thrall MA, Hamar DW. Safety and efficacy of high-dose fomepizole compared with ethanol as therapy for ethylene glycol intoxication in cats. J Vet Emerg Crit Care (San Antonio). 2010;20(2):191-206. PMID 20487247. Abstract: interventions and results. Checked 2026-10-26.
● RELATED ANSWERS
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● FAQ
Is it too late after 4 hours in a cat?
In the prospective feline study, every cat treated with fomepizole within 3 hours survived; cats treated at 4 hours developed acute renal failure whether given fomepizole or ethanol.
When is the ethylene glycol test useful?
Between 1 and 10 to 14 hours after ingestion. Its 20 mg/dL detection limit equals the lethal level for cats; the dog lethal level is 50 mg/dL.
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