Acetaminophen
N-acetyl-p-aminophenol
Also known as: Tylenol · Paracetamol · MAPAP · N-acetyl-p-aminophenol
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 |
|---|---|---|---|---|---|
| Analgesic | 15 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Analgesic | 10 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Analgesic | 10-15 mg/kg PO q12h | PO | q12h | 5 days | 🌎 NA |
| Treatment of degenerative myelopathy (in German Shepherds) | 5 mg/kg PO (not to exceed 20 mg/kg per day) | PO | Daily | — | 🌎 NA |
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Analgesic (Rabbits) | 1-2 mg/mL in drinking water | PO | Ad libitum | — | 🌎 NA |
| Analgesic (Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas) | 1-2 mg/mL in drinking water | PO | Ad libitum | — | 🌎 NA |
- Analgesic (Rabbits): Using Children's Tylenol. Effective for controlling low-grade nociception.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Acetaminophen (paracetamol) is a synthetic non-opiate analgesic and antipyretic.
Clinical Pearls & Veterinary Context:
- Extremely toxic to cats and ferrets at any dose due to their deficiency in the enzyme glucuronyl transferase, leading to the accumulation of the toxic metabolite NAPQI.
- Occasionally used in dogs and small mammals for mild to moderate pain, particularly when NSAIDs are contraindicated (e.g., renal dysfunction).
- Lacks significant peripheral anti-inflammatory activity and does not inhibit platelet function at clinical doses.
- Often formulated in combination with opioids (e.g., codeine, hydrocodone) for synergistic analgesia.
Mechanism of action
Produces analgesia and antipyresis via weak, reversible, isoform-nonspecific inhibition of cyclooxygenase (COX-3 / COX-1-v1) in the central nervous system.
Mechanism Pathway: Inhibition of central COX enzymes → decreased prostaglandin synthesis in the CNS → elevation of the pain threshold and alteration of the hypothalamic thermoregulatory center → analgesia and antipyresis.
Note: It lacks significant peripheral COX-1 or COX-2 inhibition, which explains its lack of anti-inflammatory and anti-platelet effects.
Safety & warnings
Contraindications
- Cats (at any dosage)
- Ferrets
- Sugar Gliders
- Hedgehogs
Adverse effects
- Methemoglobinemia (especially in cats and dogs at high doses)
- Hepatotoxicity (liver necrosis)
- Renal effects
- Gastrointestinal disturbances
- Facial and paw swelling (edema)
- Keratoconjunctivitis sicca (KCS)
- Cyanosis
- Hypothermia
Precautions
WARNINGS:
- ABSOLUTELY CONTRAINDICATED IN CATS AND FERRETS. Severe methemoglobinemia, hematuria, icterus, and death can occur.
- Dogs do not metabolize acetaminophen as well as humans; use judiciously to avoid methemoglobinemia and hepatotoxicity.
- Not recommended during the immediate post-operative phase (first 24 hours) in dogs due to increased risk of hepatotoxicity.
- Use cautiously in pregnant animals (FDA Category B in humans, Papich Class C in veterinary).
Drug interactions
Chronic use with acetaminophen may lead to renal pathologies
Increased conversion of acetaminophen to hepatotoxic metabolites; potentially increased risk for hepatotoxicity
May deplete hepatic glutathione, thereby leading to increased hepatic toxicity
Not recommended for postoperative analgesia in animals that received halothane anesthesia
Possible increased risk of hepatotoxicity
Possible increased risk for hypothermia
May increase the severity of acetaminophen-induced methemoglobinemia or Heinz body formation
Large doses may potentiate anticoagulant effects
Monitoring
- Liver enzymes (ALT, AST, ALP)
- Renal function (BUN, Creatinine)
- Hematologic parameters (CBC for methemoglobinemia or Heinz bodies)
- Clinical signs of toxicity (edema, cyanosis, lethargy)
Pharmacokinetics
Absorption
In humans, rapidly and nearly completely absorbed from the gut.
Distribution
Rapidly distributed into most tissues. Approximately 25% is plasma protein bound. Excreted in milk in low concentrations.
Metabolism
Dogs exhibit dose-dependent (saturable) metabolism. Cats are unable to significantly glucuronidate acetaminophen, leading to the formation of toxic metabolites (NAPQI).
Elimination
Primarily hepatic metabolism followed by renal excretion of metabolites.
Overdose
Acute Toxicity & Overdose:
- Clinical Signs: Methemoglobinemia (brown blood/mucous membranes), liver necrosis, renal effects, facial and paw swelling, keratoconjunctivitis sicca (KCS), vomiting, lethargy, cyanosis, hypothermia.
- Species Differences: Liver effects are more common in dogs; facial/paw swelling and methemoglobinemia are more common in cats.
- Treatment: Standard gut emptying techniques (emesis/lavage) and activated charcoal if recent. Administer acetylcysteine (NAC) as a glutathione precursor to bind toxic metabolites. Supportive care includes s-adenosyl methionine (SAMe), oxygen therapy, IV fluids, and blood transfusions or methylene blue for severe methemoglobinemia.
Available products
Formulations
- chewable tablets
- extended release tablets
- caplets
- gelcaps
- sprinkle capsules
- drops
- elixirs
- liquids
- solutions
- suppositories
Veterinary
- None
Human-labeled
- Acetaminophen Tablets: 325 mg, 500 mg, 650 mg
- Chewable Tablets: 80 mg
- Extended Release Tablets: 650 mg
- Caplets: 160 mg, 500 mg, 650 mg
- Gelcaps: 500 mg
- Capsules: 325 mg, 500 mg
- Sprinkle Capsules: 80 mg, 160 mg
- Drops: 80 mg/0.8 mL
- Elixirs: 80 mg/2.5 mL, 80 mg/5 mL, 120 mg/5 mL, 160 mg/5 mL
- Liquids/Solutions: 160 mg/5 mL, 500 mg/15 mL, 100 mg/mL
- Suppositories: 80 mg, 120 mg, 125 mg, 300 mg, 325 mg, 650 mg
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at temperatures less than 40°C. Do not freeze oral solutions or suspensions.
Client information
CRITICAL WARNING: Never give this medication to cats or ferrets under any circumstances. It is highly toxic and often fatal to these species.
- For Dogs: Follow your veterinarian's directions carefully. Do not exceed the prescribed dosage or increase the dosing frequency, as overdoses can cause severe liver damage.
- Keep all medications strictly out of reach of children and pets.
- Contact your veterinarian immediately if you notice vomiting, lethargy, swelling of the face or paws, or dark/discolored gums.
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.