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Poisonous to: Cats, Dogs

Level of toxicity: Generally moderate to severe

Common signs to watch for:

  • Lethargy
  • Swelling of the face/paws
  • Difficulty breathing
  • Brown/blue gums
  • Vomiting
  • Inappetance/anorexia
  • Black-tarry stool
  • Jaundice

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Acetaminophen, a cyclooxygenase (COX)-3 inhibitor, is a popular OTC analgesic and antipyretic medication used frequently in humans. While this drug is very safe for human use, it has a narrow margin of safety in dogs and cats; the severity of poisoning and development of clinical signs is species-dependent. Cats, who have an altered liver metabolism (specifically, glucuronidation), have a decreased ability to metabolize acetaminophen, making them much more susceptible to poisoning. In cats, poisoning results in severe red blood cell (RBC) injury in the form of methemoglobinemia (metHb). In cats, clinical signs of lethargy, swelling of the face or paws, difficulty breathing, brown or blue gums, vomiting, and not wanting to eat may be seen. In dogs, keratoconjunctivitis sicca (dry eye), liver failure, and RBC injury may be seen. In dogs, clinical signs of weakness, lethargy, not wanting to eat, vomiting, black-tarry stool, and jaundice skin may be seen. Treatment includes decontamination, fluid therapy, provision of a glutathione source (S-adenosyl-methionine or SAMe), and the antidote, N-acetylcysteine. Blood work should be frequently performed to monitor for RBC injury or liver failure. Generally, prognosis is fair with therapy. Those with severe hepatic failure have a poorer prognosis.

Poison type: Medications

Alternate names: Tylenol, paracetamol, APAP