Acetaminophen (Tylenol) is a common drug used to treat mild to moderate pain and fever. It does not relieve redness, stiffness or swelling of joints or tissue inflammation. It is not an FDA-approved medication for pets. The toxic metabolites are converted to non-toxic ones through a series of reactions involving enzymes called glucuronyl transferases. Cats are deficient in these enzymes, therefore the use of acetaminophen is very dangerous because cats have a limited ability to metabolize acetaminophen to non-toxic metabolites. In other animal species, including humans, the toxic metabolites are eliminated from the blood by the kidneys, but in cats they remain in the blood and liver causing severe damage to red blood cells and liver failure. Signs of red blood cell damage include respiratory distress, weakness, depression, dark brown, pale, or bluish mucus membranes, dark urine, and swollen face and paws. Affected cats should be adequately hydrated and kept warm. In cases of severe anemia blood transfusion may be required.
Antidotal therapy must be administered by a veterinary specialist; this includes the following medications:
- Ascorbic Acid
- Sodium Sulfate
Treatment with N-acetylcysteine is most effective if administered within 8 hours of ingestion. Treatment within 24 hours of exposure may save the cat, but liver damage may occur.4 Pet owners also should be aware that ferrets have the same problem converting this drug to non-toxic metabolites and are susceptible to the same adverse reactions as cats. Prognosis depends upon the total dose ingested and the time to treatment. Treatment is usually successful when administered before the signs develop. Cats with severe hemolytic anemia have a more guarded prognosis.5
- Alexander Campbell, Michael Chapman. Handbook of Poisoning in Dogs and Cats
- Debra Eldredge D.V.M. Pills For Pets.
- Andrew L. Allen. The diagnosis of acetaminophen toxicosis in a cat.
- Ramesh Chandra Gupta. Veterinary toxicology: basic and clinical principles.
- Elizabeth Rozanski, John Edward Rush. A color handbook of small animal emergency and critical care medicine.