VETINUITY
Why are cats so sensitive to acetaminophen?
Cats have limited glucuronide conjugation, so more of the drug goes to the toxic metabolite. Methemoglobinemia appears within a few hours, followed by Heinz bodies.
● ANSWER
Sourced & dated
How much acetaminophen is toxic to cats and dogs, and what is the NAC dose?
Cats are poisoned at 40-50 mg/kg and can show signs at 10 mg/kg; dogs above 100 mg/kg. Treat with N-acetylcysteine 140 mg/kg IV or PO, then 70 mg/kg PO every 6 hours for 5 to 7 more doses.
● VETINUITY ACETAMINOPHEN EXPOSURE CALCULATOR
Vetinuity acetaminophen exposure calculator
Bands name the species they apply to. Repeated doses lower every threshold.
● WHAT'S DOCUMENTED
Vetinuity’s acetaminophen table: cats are poisoned at 40-50 mg/kg and have shown signs at 10 mg/kg, dogs show signs above 100 mg/kg and methemoglobinemia above 200 mg/kg, and both are treated with N-acetylcysteine 140 mg/kg IV or PO as a 5% solution, then 70 mg/kg PO every 6 hours for 5 to 7 more doses. The Vetinuity acetaminophen exposure calculator above turns tablets or millilitres of liquid into mg/kg and names the band for each species. Brian Toncray, DVM, an emergency veterinarian, put this table into Vetinuity because a single 325 mg tablet is about 80 mg/kg for a 4 kg cat.
Treatment doses
| Drug | Dose | Route and timing |
|---|---|---|
| N-acetylcysteine, loading | 140 mg/kg of a 5% solution | IV or PO once |
| N-acetylcysteine, maintenance | 70 mg/kg | PO every 6 h for 5 to 7 more doses |
| Ascorbic acid | 30 mg/kg | PO or IM every 6 h for 6 to 8 doses |
| Methylene blue | 1-1.5 mg/kg of a 1% solution | IV over several minutes |
| Maropitant | 1 mg/kg | SC, IV or PO every 24 h as needed |
| Ondansetron | 0.5-1 mg/kg | IV or PO every 12 h as needed |
SAMe, alone or with silybin, has been suggested as an adjunct. Give fluids and blood transfusions as needed.
What it looks like
In cats: brown or muddy mucous membranes from methemoglobinemia, tachycardia, hyperpnea, facial or paw edema, cyanosis, dyspnea, hypothermia and vomiting, with Heinz body anemia following. In dogs: hepatotoxicity, icterus and necrosis are the bigger concern, and repeated dosing produces toxicosis at lower amounts than a single ingestion. Kidney injury is possible in both.
Decontamination
Induce emesis in a patient that is still normal, then give a single dose of activated charcoal with a cathartic.
Working an exposure
A 4 kg cat that chewed one 80 mg chewable has taken 20 mg/kg, already above the lowest dose that has produced signs in cats. A 20 kg dog that ate four 500 mg tablets has taken 100 mg/kg, the point where canine signs begin. Both need decontamination and NAC; the cat also needs methemoglobin watched from the first hours.
Also see NSAID overdose, permethrin in cats and transfusion volumes.
● SOURCES
- 1. Merck Veterinary Manual: Toxicoses From Human Analgesics in Animals. Acetaminophen: clinical findings and treatment. Checked 2026-10-26.
● RELATED ANSWERS
- Ibuprofen and NSAID Overdose in Dogs: Toxic Doses
Ibuprofen causes GI signs in dogs from 100-125 mg/kg, renal failure from 175-300 mg/kg, CNS signs above 400 mg/kg and can be lethal above 600 mg/kg; naproxen is toxic at far lower doses.
- Permethrin Toxicity in Cats: Methocarbamol and ILE
Control tremors with methocarbamol 55-220 mg/kg IV or diazepam 0.2-2 mg/kg IV, bathe with mild detergent and cool water, and consider 20% lipid emulsion at 1.5 mL/kg then 0.25 mL/kg/min.
- Lily Toxicity in Cats: Time and Fluid Management
Suspected true-lily or daylily exposure in a cat requires urgent veterinary assessment because renal injury can follow; early treatment matters before kidney dysfunction develops.
- Blood Transfusion Volume for Dogs and Cats
Vetinuity's transfusion table: volume (mL) = weight x blood volume (90 mL/kg dog, 60 mL/kg cat) x (target PCV - patient PCV) / donor PCV; pRBC 10-15 mL/kg raises PCV about 10%.
- Xylitol Toxicity in Dogs: Treatment
Canine xylitol toxicity: insulin-mediated hypoglycemia and hepatopathy, with decontamination, monitoring, and prognosis from published case series.
● FAQ
How do dogs differ?
Dogs show signs above 100 mg/kg and methemoglobinemia above 200 mg/kg, and they more often develop icterus and hepatic necrosis than cats.
What concentration of NAC do I give IV?
Dilute the 10% or 20% product to a 5% solution in 5% dextrose or sterile water before IV use.
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