Tylenol is very toxic in cats; one adult tablet is very poisonous and ingestion of two tablets is fatal

Clinical signs of weakness, pale gums, swelling of the face and red colored urine are common signs that may occur within 4 hours of ingestion

An antidote is available to treat this type of toxicity

Our emergency service is available 24 hours daily, seven days a week, to treat any type of emergency situation, including acetaminophen toxicity

What is acetaminophen toxicity?

• Acetaminophen can be found in Tylenol products and many other pain relievers.  
• Toxicity occurs primarily in cats because of a limited ability to metabolize acetaminophen, but can also occur in dogs
• Effects seen in liver, red blood cells and hemoglobin (protein in red blood cells responsible for carrying oxygen)
• Toxic effects include:
• liver damage
• anemia (low red blood cells in the bloodstream)
• methemoglobinemia (abnormal hemoglobin which has a decreased ability to carry oxygen in the bloodstream)
• Toxic dose:
• Cats – 50 milligrams per kilogram body weight
• Dogs – 150 milligrams per kilogram body weight

Clinical signs

• Clinical signs can occur within 4 hours of ingestion of acetaminophen
• Pale, white or blue-tinged mucous membranes (the gums are the best place to look for this)
• Red or brown-tinged urine
• Swelling of the face and front legs in cats, accompanied by increased tear production and itchiness
• Anorexia, salivation, vomiting
• Abdominal pain can be seen in dogs
• Depression, weakness and coma can occur

Diagnosis

• History of ingestion of acetaminophen
• Clinical signs
• Laboratory tests
• Methemoglobinemia (abnormal hemoglobin) causing the blood to be dark brown in color
• Heinz body anemia (decreased red blood cells in the blood due to abnormal accumulation of hemoglobin in the red blood cells)
• Increased liver enzymes
• Decreased blood glutathione levels (used in metabolism of acetaminophen)

Treatment

• The patient may require hospitalization for 72 hours or more.
• If the animal is seen within 4 hours of ingestion:
• Vomiting should be induced to attempt to empty the stomach contents.
• Gastric lavage, under light anesthesia, can also be done to empty the stomach contents.
• Administration of activated charcoal can help to decrease absorption of acetaminophen from the gastrointestinal tract.
• Supportive treatment
• Oxygen therapy
• Intravenous fluids
• A blood transfusion may be necessary
• Feed cats kitten food, which is high in sulfhydryl group substrates.   This will aid in metabolism of the acetaminophen.
• There is an antidote to acetaminophen called N-acetylcysteine.
• Vitamin C can help slowly decrease the amount of abnormal hemoglobin in the bloodstream.
• Cimetidine (Tagamet) helps to reduce metabolism of acetaminophen by the liver.

Complications

• Death can occur in cats within 18-36 hours after ingestion due to abnormal hemoglobin.
• Death can occur in dogs within 2-5 days after ingestion due to liver damage.
• Clinical signs should last 24-48 hours.

Aftercare

• Aftercare is generally not needed if clinical signs resolve.   Follow-up care with your regular veterinarian may be needed to evaluate severity and chronicity of liver damage.

Prognosis

• Prognosis depends on the dose of acetaminophen ingested and how quickly the animal is seen by a veterinarian.   Progressively increasing liver enzymes or methemoglobin levels are serious signs.
• Methemoglobin levels greater than 50% is a grave prognostic indicator.

References

• Osweiler, Gary D.  Toxicology.   Lippincott, Williams and Wilkins.   New York, 1996.
• Plunkett, Signe J.   Emergency Procedures for the Small Animal Veterinarian.   WB
• Saunders.   New York, 2000.
• Tilley, Lawrence P.   The 5-Minute Veterinary Consult: Canine and Feline.   Lippincott, Williams and Wilkins. New York, 2003.