Tylenol poisoning in dogs | Dr. Justine Lee, DACVECC, DABT, Board-certified Veterinary Specialist

Posted by justinelee in Animal Safety, Blog

According to the ASPCA Animal Poison Control Center, Tylenol, the brand name for the over-the-counter (OTC) pain medication acetaminophen, is one of the top 10 causes for poisoning in dogs and cats. (BTW, if you live in another country, this is called paracetamol instead). This popular anti-fever medication is commonly found in households, as it’s very safe for humans (even pregnant women!). However, it can be very poisonous to cats, ferrets, and even dogs, depending on what dose is ingested.

When it comes to poisoning, it’s the “dose that makes the poison.” Sometimes, we will prescribe Tylenol with codeine in dogs with severe pain. At appropriately prescribed doses, this can be safe… that is, in dogs ONLY. Tylenol should NEVER be used in cats, as cats can develop clinical signs of poisoning at very low doses. In dogs, we typically use low dose (e.g., 10-15 mg/kg orally every 8-12 hours). This same dose is very poisonous in cats! That’s because some species metabolize drugs differently, resulting in poisoning at different doses.

More importantly, know that dogs and cats develop different types of poisoning from acetaminophen. In dogs, acetaminophen poisoning can cause elevated liver enzymes and progress to liver failure, while in cats, it causes an abnormal ability for red blood cells (RBCs) to carry oxygen (due to methemoglobinemia), resulting in life-threatening low oxygen levels. This can be seen in dogs too, with massive ingestions > 200 mg/kg.

Breeds predisposed
While there are no specific breeds predisposed to acetaminophen poisoning, again, cats are very susceptible to poisoning due to their altered liver function (called glucuronidation). That’s why poisoning can be seen at such low doses in cats (as low as 10 mg/kg). That’s different than dogs, where the toxic dose is approximately 10X higher at 100-150 mg/kg).1 So, it takes LESS than one Tylenol tablet to potentially kill a cat.

Clinical signs
So, if your dog or cat gets into Tylenol, what signs will you see? Again, this will differ between dogs and cats. Signs of Tylenol poisoning in a cat include:

• Inappetance progressing to complete anorexia
• Lethary
• Hiding or lying in unusual places (e.g., closet, basement, etc.)
• Acute swelling of the paws and face
• Difficulty breathing (including an elevated respiratory rate > 40 breaths per minute, open mouth breathing, blue-colored gums/cyanosis, etc.)
• Vomiting
• Death

Signs of Tylenol poisoning in dogs include:

• Inappetance progressing to complete anorexia
• Weakness or malaise
• Gastrointestinal signs (e.g., drooling, vomiting)
• Yellow or jaundiced gums
• Difficulty breathing (including an elevated respiratory rate > 40 breaths per minute, open mouth breathing, blue- or brown-colored gums/cyanosis, etc.)
• Black-tarry stool (called melena)
• Neurologic signs (e.g., walking wobbly, seizures, coma)
• Dry eye (chronic squinting and abnormal green discharge of the eyes)
• Death

Diagnosis
How to we diagnose Tylenol poisoning? Typically this is based on you – the pet owner – telling us. If you find a chewed bottle or accidentally gave it to your pet, call the ASPCA Animal Poison Control center or your veterinarian immediately for life-saving advice. We can potentially measure acetaminophen levels at a local human hospital, but this isn’t readily available and will cost you quite a bit of money. So when in doubt, fess up fast if you do know.

Treatment
If your dog or cat got into acetaminophen, contact your veterinarian or the ASPCA Animal Poison Control Center (this is the only non-profit APCC in the world) immediately to identify if it was a poisonous amount. If a toxic dose was ingested, seek immediate veterinary attention – at your veterinarian or an emergency veterinarian. Unfortunately, with acetaminophen poisoning, it’s often too late to induce vomiting, since acetaminophen is rapidly absorbed from the stomach (especially if it’s a gel cap). So, instead of trying to induce vomiting at home, go immediately into your veterinarian for life-saving care.

Once you are at your veterinary clinic, treatment for Tylenol poisoning may include:

• Activated charcoal (to help bind up any residual acetaminophen in the stomach and intestines)
• Anti-vomiting medication (so your pet holds down the charcoal and the antidote for acetaminophen)
• Blood work to monitor the liver enzymes, the RBC count, to look for the presence of methemoglobinemia
• Oxygen therapy (especially in cats having difficulty breathing)
• Drugs that protect the liver (specifically SAMe)
• The antidote for acetaminophen: n-acetylcysteine (often abbreviated as NAC)
• Intravenous fluids to hydrate your dog or cat
• Monitoring of oxygen levels and blood pressure
• Blood transfusions, if needed
• Supportive care

Most importantly, know that acetaminophen poisoning has an antidote: n-acetylcysteine. While not all veterinarians carry this antidote, most veterinary specialty hospitals and emergency hospitals do. Treatment for at least two days is typically necessary when toxic doses of acetaminophen are ingested.

Prevention
When in doubt, always keep OTC and prescription medications out of reach. Simply putting away your backpack, briefcase, or your purse may help prevent accidental poisoning. Also, never administer a medication to your pet without checking with your veterinarian or the ASPCA APCC first.

Prognosis
Thankfully, with appropriate therapy, the prognosis for acetaminophen poisoning is typically fair to good. When in doubt, if you suspect your pet got into acetaminophen, contact your veterinarian, the ASPCA APCC, or emergency veterinarian right away and seek immediate veterinary attention (yes, even in the middle of the night).

Keep in mind that with any poisoning, the sooner you seek attention, the better the prognosis and the less costly to you. More importantly, the less damage occurs to your pet the sooner your veterinarian can treat it!

References:
1. Babski DM, Koenig A. Acetaminophen. In Blackwell’s Five-Minute Veterinary Consulting Clinical Companion: Small Animal Toxicology. Wiley-Blackwell, Ames. 2011:pp263-269.
2. Oehme FW. Acetaminophen toxicity. In Blackwell’s Five-Minute Veterinary Consult: Canine & Feline. Eds. Tilley LP, Smith FWK. 2007, 4th ed. Blackwell Publishing, Ames, Iowa. pp. 10-11.