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Have a headache?
Before you reach for Tylenol, make sure that you keep that bottle out of reach of your dog or cat! Tylenol contains the active ingredient acetaminophen (often called paracetamol in other countries), and is a popular over-the-counter (OTC) pain medication and anti-fever medication used by humans. While this drug is very safe for human use, it has a narrow margin of safety in dogs and cats.
Unfortunately, when dogs and cats ingest acetaminophen – either accidentally or because their pet owner inadvertently gave it to them, they can develop poisoning at low doses. The severity of acetaminophen poisoning depends on the species, as dogs and cats develop different clinical signs and problems with poisoning.
Because cats have altered liver metabolism (called glucuronidation), they metabolize acetaminophen poorly, making them much more susceptible to poisoning. The toxic dose of acetaminophen in cats is very low, seen at as little as 10 mg/kg. This means that as little as one Tylenol tablet could kill a cat.
In cats, acetaminophen poisoning affects the red blood cells (RBC). Cats develop methemoglobinemia (metHb), which means that their red blood cells can’t carry oxygen. As a result, clinical signs of poisoning in cats include:
- Swelling of the face or paws
- Difficulty breathing
- An increased respiratory rate
- Open mouth breathing
- Abnormal colored gums (from blue to brown instead of pink)
- Liver failure (less common)
In dogs, the toxic dose of acetaminophen poisoning is seen > 100 mg/kg. Dogs typically develop liver failure from acetaminophen, and with massive ingestions, methemoglobinemia (abnormal hemoglobin that can’t carry oxygen in the body) can also be seen. Clinical signs of acetaminophen poisoning in dogs include:
- Dry eye (chronic squinting and abnormal green discharge of the eyes)
- Black-tarry stool
- Jaundiced gums
- Increased liver enzymes
- Walking drunk
If your dog or cat gets into acetaminophen, it’s typically too late to induce vomiting, as the drug is rapidly absorbed from the stomach. Instead, treatment includes the following at your veterinary clinic:
- Activated charcoal to bind up the poison from the stomach and intestines
- Blood work to evaluate the RBC count, to look for the presence of methemoglobinemia, and to monitor the liver values
- IV fluids
- Liver protectants (such as SAMe, n-acetylcysteine)
- Oxygen therapy, if needed
- Blood transfusions, if needed
- Monitoring of oxygen levels and blood pressure
- Symptomatic supportive care
Thankfully, with acetaminophen poisoning, there’s an antidote called n-acetylcysteine (often abbreviated as NAC). Not all veterinarians carry this antidote, so if your pet got into a toxic amount of acetaminophen, referral to an emergency hospital or specialty clinic may be necessary.
The prognosis for acetaminophen poisoning is typically fair to good with supportive care and the use of the antidote. When in doubt, if you suspect your dog or cat got into acetaminophen, contact your veterinarian or emergency veterinarian right away and seek immediate veterinary attention (yes, even in the middle of the night). With any poisoning, the sooner you seek attention, the better the prognosis and the less costly or damaging to you and your pet.
If you have any questions or concerns, you should always visit or call your veterinarian – they are your best resource to ensure the health and well-being of your pets.
Acetaminophen (Tylenol) Toxicity
My client, Ann, was dismayed when I told her that my physical examination and blood tests failed to reveal why Oscar, her 10 year-old talkative Siamese cat, had recently taken to loudly vocalizing in the middle of the night. Siamese cats have a reputation for being garrulous, and Ann had always found this charming. But not at three o’clock in the morning.
“This has been going on for almost a week now”, said Ann, through bloodshot eyes. “I’m trying to recover from a cold, and I really need a good night’s sleep. Last night I took Nyquil®, and slept through most of Oscar’s howling. I’m tempted to give a little to Oscar, so maybe he’ll sleep through the night as well”, she told me. I was shocked. “Nyquil contains acetaminophen!” I told Ann. “If you give Nyquil® to Oscar”, he may fall into a sleep that he never wakes up from!”
Ann prefers that I not use her last name in this article she is embarrassed, as a cat owner, that she didn’t know that acetaminophen is very toxic to cats. She shouldn’t be. Despite the dangers of acetaminophen being published in numerous journals and magazines, many cat owners and enthusiasts still are unaware of how toxic this drug can be to cats, or that many common over-the-counter (OTC) drugs contain acetaminophen as one of their main ingredients.
Companion animals are at risk for developing toxicosis to prescription drugs as well as over-the-counter (OTC) medications, either by deliberate administration of the medication by owners, or by accidental consumption of improperly stored drugs. Dogs are more likely to chew on pill vials or tubes of ointment, eating the pills or ointment when the container finally breaks open. Cats, on the other hand, are generally more discrete about what they put in their mouths and are less likely to voluntarily ingest medications. With cats, toxicity tends to occur when well-intentioned owners unknowingly administer a seemingly harmless OTC medication, often with devastating results.
Veterinarians occasionally use OTC drugs to treat a variety of their patients’ maladies. The most common of these are probably the non-steroidal anti-inflammatory drugs (NSAIDs). We prescribe these to treat musculoskeletal inflammation and pain, control fevers, and sometimes to inhibit blood clotting. Aspirin is clearly the best known of the NSAIDs. Aspirin is a non-steroidal anti-inflammatory drug (NSAID) that, for many years, had been used to control musculoskeletal pain and inflammation in dogs, and sometimes cats. In recent years, a multitude of safer and more effective oral pain relievers have been developed, making aspirin an uncommon first choice for joint and skeletal disease in companion animals. In cats, we still use aspirin occasionally, mainly to inhibit blood clotting. Cats with certain heart diseases like hypertrophic cardiomyopathy are at increased risk for developing dangerous blood clots. Aspirin is frequently prescribed in an effort to inhibit blood clot formation, however, the dose must be strictly adhered to. Acetaminophen is often grouped with the NSAIDs, although technically it is somewhat different. “Veterinarians occasionally prescribe low doses of acetaminophen for pain control in dogs, but never for cats” says Dr. Jill Richardson, consulting editor of toxicology for the Veterinary Information Network and Director of Consumer Relations and Technical Services for Hartz. “In dogs, the dose is 5 – 10 mg per kg. Dogs show signs of toxicity when the dose exceeds 75 mg per kg.” Cats, however, are very sensitive to acetaminophen toxicity. “There have been reports of toxicity developing in cats at doses as low as 10 mg/kg.” Acetaminophen is one of the top two most common household medications, and it is no surprise that acetaminophen toxicity is commonly reported. In fact, between January 1998 and March 2000, veterinarians at the ASPCA Animal Poison Control Center consulted on over 1050 cases of accidental exposure to acetaminophen in dogs and cats.
Although most readily recognized by the trade name Tylenol, acetaminophen is the major ingredient of most aspirin-free pain relievers and cold remedies, including Excedrin®, Panadol®, Anacin®, Midol®, Pamprin®, BromoSeltzer®, and Percogesic®. Many decongestant products and “cold” or “flu” formulas also contain acetaminophen. For example, a single adult dose of Nyquil® syrup contains 1000 milligrams of acetaminophen, the equivalent of more than three Tylenol tablets. This is a frighteningly large dose, considering that ingestion of one 325-mg tablet by a cat results in severe toxicosis, and two tablets ingested within 24 hours is fatal. “Any dose is potentially life-threatening to a cat” says Dr. Richardson.
The enzymes responsible for the metabolism of most drugs are found in the liver. One particular enzyme, called glucuronyl transferase, is responsible for attaching a large molecule called glucuronide to a drug, rendering the drug inactive and water-soluble. The process of attaching a large molecule to a drug is called “conjugation”. Cats, as a species, have low levels of glucuronyl transferase. Thus, many drugs that are quickly excreted as glucuronyl conjugates in other species are very slowly removed from the bloodstream in cats. Toxic metabolites accumulate in the bloodstream, causing severe organ damage.
At toxic doses, acetaminophen often causes hepatic necrosis – death of liver cells – especially in dogs. Cats, however, are more likely to develop a condition called methemoglobinemia, in which there is an excess amount of methemoglobin in the bloodstream. Methemoglobin is an abnormal form of hemoglobin that is incapable of transporting oxygen. As methemoglobin levels start to rise, clinical signs develop, such as chocolate-brown mucous membranes, fast heart rate, labored breathing, depression, vomiting, edema (swelling) of the face, neck and limbs, hypothermia, ataxia (incoordination) and coma. Cats may become jaundiced as liver failure develops.
Treatment for acetaminophen toxicity involves providing supplemental oxygen, administering intravenous fluids, and giving several drugs intravenously, including vitamin C, cimetidine (Tagamet), and N-acetylcysteine, a drug that provides the body with excessive amounts of the amino acid cysteine. This amino acid is necessary for the liver to repair itself and counteract acetaminophen’s toxic effects. Time is of the essence in treating acetaminophen toxicity. Treatment tends to be less efficacious when initiated more than 8 hours after ingestion.
Other over-the-counter NSAIDs such as ibuprofen (Advil®, Nuprin®, Motrin®) or naproxen (Aleve®) should never be given to cats. Ibuprofen has a narrow margin of safety in dogs, and cats, with their inability to metabolize these drugs, are thought to be twice as sensitive as dogs to ibuprofen’s toxic effects.
Ultimately, any oral medication can potentially cause toxicosis in companion animals, especially cats, with their small body size and unique metabolic pathways. Cat owners should be certain to keep all medications safely stored, and have the phone number of their veterinarian and national poison control center readily accessible in case of a toxin-related emergency. No product, over-the-counter or otherwise, should be given to a cat without the advice of a veterinarian.
Sidebar 1: What to do if you suspect acetaminophen toxicity
“Acetaminophen toxicity is an emergency situation” says Dr. Jill Richardson, Director of Consumer Relations and Technical Services for Hartz, and consulting editor for toxicology for the Veterinary Information Network. “You should contact your veterinarian immediately, even if the cat ate only one pill, or even if the owner simply suspects that it was eaten. Early aggressive treatment by a veterinarian is extremely important.Even if you only suspect your cat may have eaten an acetaminophen tablet, still see a vet immediately. There is a test that can confirm exposure, but treatment for poisoning should be initiated while you wait for test results to see if the cat was actually exposed.”
Sidebar 2: Clinical signs of acetaminophen toxicity
Swollen face, neck and limbs
Hypothermia (low body temperature)
Acetaminophen is a synthetic nonopiate derivative of p-aminophenol widely used in people for its antipyretic and analgesic properties. Its use has largely replaced salicylates because of the reduced risk of gastric ulceration.
Acetaminophen is rapidly absorbed from the GI tract. Peak plasma concentrations are usually seen within an hour but can be delayed with extended-release formulations. It is uniformly distributed into most body tissues. Protein binding varies from 5%–20%. The metabolism of acetaminophen involves two major conjugation pathways in most species. Both involve cytochrome P450 metabolism, followed by glucuronidation or sulfation.
Cats are more sensitive to acetaminophen toxicosis, because they are deficient in glucuronyl transferase and therefore have limited capacity to glucuronidate this drug. In cats, acetaminophen is primarily metabolized via sulfation when this pathway is saturated, toxic metabolites are produced. In dogs, signs of acute toxicity are usually not seen unless the dosage of acetaminophen exceeds 100 mg/kg. Clinical signs of methemoglobinemia have been reported in 3 of 4 dogs at 200 mg/kg. Toxicity can be seen at lower dosages with repeated exposures. In cats, toxicity can occur with 10–40 mg/kg.
Methemoglobinemia and hepatotoxicity characterize acetaminophen toxicosis. Renal injury is also possible. Acute keratoconjunctivitis sicca has been reported in some dogs after acetaminophen ingestion. Cats primarily develop methemoglobinemia within a few hours, followed by Heinz body formation. Methemoglobinemia makes mucous membranes brown or muddy in color and is usually accompanied by tachycardia, hyperpnea, weakness, and lethargy. Other clinical signs of acetaminophen toxicity include depression, weakness, hyperventilation, icterus, vomiting, hypothermia, facial or paw edema, cyanosis, dyspnea, hepatic necrosis, and death. Liver necrosis is more common in dogs than in cats. Liver damage in dogs is usually seen 24–36 hr after ingestion. Centrilobular necrosis is the most common form of hepatic necrosis seen with acetaminophen toxicity.
The objectives of treating acetaminophen toxicosis are early decontamination, prevention or treatment of methemoglobinemia and hepatic damage, and provision of supportive care. A Schirmer tear test (to confirm keratoconjunctivitis) can be used if necessary. Induction of emesis is useful when performed early. This should be followed by administration of activated charcoal with a cathartic. Activated charcoal may be repeated, because acetaminophen undergoes some enterohepatic recirculation.
Administration of N- acetylcysteine (NAC), a sulfur-containing amino acid, can reduce the extent of liver injury or methemoglobinemia. NAC provides sulfhydryl groups, directly binds with acetaminophen metabolites to enhance their elimination, and serves as a glutathione precursor. It is available as a 10% or 20% solution. The loading dose is 140 mg/kg of a 5% solution IV or PO (diluted in 5% dextrose or sterile water), followed by 70 mg/kg, PO, qid for generally seven or more treatments (some authors recommend up to 17 doses). Vomiting can occur with oral NAC. NAC is not labeled for IV use however, it can be administered as a slow IV (over 15–20 min) with a 0.2-micron bacteriostatic filter. Activated charcoal and oral NAC should be administered 2 hr apart, because activated charcoal could adsorb NAC.
Liver enzymes should be monitored and rechecked at 24 and 48 hr. The animal should also be monitored for methemoglobinemia, Heinz body anemia, and hemolysis. Fluids and blood transfusions should be given as needed. Ascorbic acid (30 mg/kg, PO or injectable, bid-qid) may further reduce methemoglobin levels. Cimetidine (5–10 mg/kg, PO, IM, or IV), a cytochrome P450 inhibitor, may help reduce formation of toxic metabolites and prevent liver damage in dogs only. Cimetidine should not be used in cats. In vitro evidence indicates that use of cimetidine in cats can produce more toxic metabolites of acetaminophen . S-Adenosyl methionine has been suggested as an adjunct to manage acute or chronic hepatic injury at 18 mg/kg, PO, for 1–3 mo in dogs and cats.
Will Tylenol Kill Your Cat?
Tylenol is one of the most commonly used pain killers. It is also a killer to your cat. The primary ingredient in Tylenol is acetaminophen which is toxic to cats, even in small dosages.
Many people think that if their cat is in pain due to arthritis, surgery, or an injury that a little bit of Tylenol in their food can help take the edge off. But cats can have toxic poisoning with as little as 10 mg per body weight.
But you giving acetaminophen to your pet is not the only way he may ingest it. Pets can break into your medicine cabinet and chew through medicine bottles because they seem like fun to chew on. If you leave your medication out on the counter, you cat may get into it because she starts to bat it around. Though dogs are able to excrete acetaminophen from their body, cats cannot. Acetaminophen causes a breakdown of blood cells which causes Heinz anemia and death.
Cats are 7 to 10 times more susceptible to acetaminophen toxicity than dogs.
Signs and symptoms of Tylenol poisoning
Make sure you know the signs and symptoms of acetaminophen toxicity.
- Brownish-gray colored gums
- Brown urine
- Difficulty breathing
- Swollen Face, neck and paws
- Abnormally low body temperature (Hypothermia)
- Decrease appetite
- Jaundice- yellowish color to their skin and/or whites of their eyes
If your cat has Tylenol toxicity it needs to be treated as an emergency situation and you need to go to the vet immediately. Treatment includes oxygen to assist breathing, IV fluids, IV medication to counter act the toxicity and alleviate symptoms.
Never self diagnose your pets when it comes to their medical treatment. There are pet safe medications, make sure you talk to your vet so you know what is safe to give to your pet.