Most often Tylenol poisoning occurs when the pet ingests a pill left out or accidently dropped on the floor. Often however, a well meaning owner gives his pet a Tylenol, because of pain or discomfort.
Cats are extremely sensitive to Tylenol. As little as one half of a regular strength tablet may be toxic or fatal to a cat. Dogs can tolerate a higher dose and may even be prescribed Tylenol by their veterinarian.
Tylenol is processed in the liver where it binds to glucuronides, sulfate, or cysteine and excreted in urine. Cats and dogs have a limited ability to form these compounds. In fact, cats cannot form glucuronides at all, which is why they are much more susceptible to poisoning.
When the liver’s ability to form glucuronides is exceeded, the remaining Tylenol or acetaminophen is converted to N-acetyl-p-benzoquinone, also known as NAPQL. NAPQL binds to cellular membranes damaging and destroying liver cells, which causes liver damage and dysfunction. The accumulation of metabolites from this uses up an anti-oxidant found in red blood cells and causes hemoglobin to be converted into methemoglobin. Because methemoglobin doesn’t carry oxygen, this reduces the levels of oxygen in the blood stream. The differences in canine and feline hemoglobin also make cats more sensitive to Tylenol. The remaining hemoglobin is damaged and attached to the red blood cells’ membranes forming tiny inclusion bodies called Heinz bodies.
Symptoms of Tylenol toxicity
- Chocolate brown mucus membranes within 4-12 hours of ingestion. This is from methemoglobin and the lack of oxygen in the blood stream and tissues.
- Brown or bloody urine
- Difficulty breathing
- Depression, weakness
- Loss of Appetite
- Fluid accumulation in the face and paws
- Watery eyes
- Coma and death
Blood tests run on animals with Tylenol toxicity will show elevated liver enzymes and elevated bilirubin levels. A blood smear stained and looked at under the microscope may show Heinz bodies in the red blood cells. This liquid portion of the pet’s blood may also be yellow when separated from the blood cells.
Since acetaminophen is rapidly absorbed by the body, it is very important to start treatment right away. This includes:
- Inducing vomiting in the pet
- Orally giving activated charcoal to bind to Tylenol still left in the stomach
- Osmotic cathartics, which cause diarrhea by retaining water in the intestines
- Intravenous fluids to maintain hydration and support the pet's blood pressure
- Acetylcysteine: Provides cysteine and increases the sulfate and glutathione levels in the blood. This causes the Tylenol to bind with these instead of damaging cells.
- Ascorbic Acid: changes methemoglobin to hemoglobin
- Oxyglobin: bovine hemoglobin, which helps to increase the blood's oxygen carrying capacity
- Oxygen through a cage or nasal tubes
- Medications to control other symptoms such as seizures
Always talk to a veterinarian before giving a pet any medications. If you suspect your pet has ingested Tylenol or any other medication contact a veterinarian and pet poison control center immediately. The sooner treatment for ingestion of a medication is started, the better the pet’s chance for recovery.
Osweiler, G D. National Veterinary Medical Series: Toxicology. Media PA: Lippincott Williams and Wilkins, 1996
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