What's Wrong With Tylenol?

By Beth Guerra, DVM

When your pet is in pain, it seems reasonable to try a painkiller at home, particularly if you aren’t able to see your vet or it’s the middle of the night. You may reach for an over-the-counter medication, such as Tylenol or Advil. Most people don’t realize that cats and dogs are not just small humans; in fact, the way they metabolize certain drugs can be vastly different.

Tylenol, or acetaminophen, comes in a variety of strengths and may also be an additive in other medications such as opioids, commonly used for post-operative pain in humans. A typical Regular Strength Tylenol (325mg) can be enough to cause severe symptoms in an average sized cat. Cats are not able to tolerate acetaminophen and can develop liver or red cell damage. In severe cases, methemoglobinemia can develop, which changes the nature of red blood cells and decrease their oxygen carrying capacity in the blood. A type of anemia, known as Heinz body anemia, can also occur and can lead to the destruction of red blood cells within circulation. As a result, vital organs are deprived of oxygen. Dogs do not seem to develop this symptom, rather, they are at high risk for necrosis, or death, of the liver cells.

Symptoms progress rapidly in cats and death can occur within 36 hours if left untreated. Affected cats may exhibit lethargy or depression, vomiting, abdominal pain, or dark colored urine. The mucus membranes may appear brown or blue in color and there may be respiratory distress. Cats can also develop swelling of the face and paws. Treatment must be aggressive and is best instituted early after suspected ingestion. The prognosis is more guarded in cats due to rapid effects of the toxicity. If your pet was given this medication or inadvertently ingested some, contact your veterinarian immediately. It is best to ALWAYS call a veterinarian before giving any medication.