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Acetaminophen (Tylenol) Toxicity in Cats

By: Dr. Anne Marie Manning

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Acetaminophen is a medication commonly used to alleviate fever and pain. Common brands include Tylenol®, Percoset®, aspirin free Excedrin®, Feverall®, Liquiprin®, Panadol®, Tempra®, Pamprin®, Midol® and various sinus, cold and flu medications. It is often found in combination in cold and flui products – many of which are labeled as "aspirin-free".

Acetaminophen is available in various formulations including tablets, liquids, liquigels, rectal suppositories and chewable tablets. It also comes in a variety of strengths per unit including children's strength (80 mg), junior strength (160 mg), regular strength (325 mg), extra strength (500 mg), and various strengths of infant and children's elixirs.

Cats are much more sensitive to acetaminophen than dogs and are therefore more susceptible to acetaminophen toxicity. One regular strength acetaminophen tablet is toxic and potentially lethal to a cat.

In addition to severe liver failure, acetaminophen causes damage to red blood cells. These include:

  • Hemolysis, which is the destruction of red blood cells
  • Formation of Heinz bodies, which are defects in red cells that cause them to be removed from circulation sooner than normal
  • Formation of methemoglobin, a non-functional type of hemoglobin. Hemoglobin allows red blood cells to carry oxygen. When methemoglobin is formed, red blood cells cannot carry oxygen and the cat has difficulty breathing.

    What to Watch For

    The symptoms of acetaminophen toxicity develop in stages. Symptoms may occur more quickly or slowly depending on the amount ingested.

  • Stage 1 (0-12 hours). Symptoms include vomiting, dullness, difficulty breathing, lethargy, anorexia, weakness, development of brown-colored gums (instead of a normal pink color) and drooling.

  • Stage 2 (12-24 hours). Symptoms include swelling of the face, lips and limbs, uncoordinated movements, convulsions, coma and potential death.

  • Stage 3 (more than 24 hours). Symptoms are associated with liver failure and include a painful belly, jaundice (yellow tinge to gums, eyes and skin) and an inappropriate mental state.

    Diagnosis

    Prompt veterinary care is crucial to surviving the toxic effects of acetaminophen. If treatment is instituted soon after ingestion there is a greater chance of survival regardless of the amount ingested.

    The diagnosis of acetaminophen toxicity is generally based on physical exam findings and a history of access or exposure to acetaminophen.

    Blood levels of acetaminophen can be analyzed, but the results may not be received for hours to days. Determination of methemoglobin levels can help determine how long treatment will be necessary and may help determine prognosis. However not all veterinary clinics have the ability to measure the methemoglobin level. Methemoglobin levels can sometime be estimated by dropping a sample of blod in to white filter paper. If the blood is brownish in color, it is roughly estimated that the methemoglobin level is more than 15% (normal is less than 1%). Levels starting at 20% cause difficulty breathing and 40% can cause mental depression.

    Baseline laboratory work including a complete blood count, diagnostic profile, and urinalysis may be completed to determine your pets overall health.


    Treatment

    Treatment is typically started as soon as the diagnosis is suspected, often in the absence of diagnostic tests. Blood work may be done to evaluate the current function of the liver and the level of red blood cells and hemoglobin.

    Treatment includes:

  • Induction of vomiting may be recommend with recent exposure (within 4 hours).

  • Activated charcoal may be used to reduce the amount of acetaminophen absorbed by the stomach, if ingestion of the substance occurred within a few hours of admission to the hospital.

  • Administration of acetylcysteine (Mucomyst®) to protect the liver from the toxic effects of acetaminophen. The medication cannot reverse liver damage that has already occurred but can help reduce further damage. This is generally given every 6 hours for a total of 8 doses.

  • Cimetidine (Tagamet®) to protect the liver from ongoing damage.

  • Vitamin C to hasten elimination of the acetaminophen.

  • Hospitalization with continuous intravenous fluid therapy.

  • Oxygen support.

  • In severe cases, blood transfusions and feeding tubes may be necessary.

  • Cats intoxicated with acetaminophen are generally hospitalized for 2-4 days.

    Prognosis for survival is based on how quickly the cat receives treatment following ingestion of a toxic amount of acetaminophen.

    Prognosis

    The prognosis for acetaminophen toxicity is good if caught early in the disease. Early vomiting and decontamination with activated charcoal prior to onset of clinical signs generally provides good prognosis. Once clinical signs are present, the prognosis is variable depending on the severity of the methemoglobinemia, hemolysis and liver damage.

    Home Care and Prevention

    There is no home care for acetaminophen toxicity. If you suspect that your cat has ingested a toxic amount of acetaminophen (for a cat this is one pill), contact your family veterinarian or local veterinary emergency facility immediately.

    After surviving acetaminophen toxicity, permanent liver damage may have occurred. Special diets and possibly lifetime medications may be needed to counteract the liver damage.

    The best preventative care is to give your cat medications only as directed by your veterinarian. Medications that may be safe for people can be fatal to cats. Also, make sure that all medications are kept out of the reach of inquisitive cats. Keeping medicine safely stored away can prevent many tragedies.

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