Veterinary Case Report: Suspected Acetaminophen (Tylenol®) Ingestion in a Cat Presenting Complaint

Recently we had a 5 year old male neutered domestic short hair cat present for possible Tylenol ingestion. The owners saw the cat near a capsule and soon after noticed he was foaming at the mouth. They looked but then couldn’t find the capsule. Knowing how serious Tylenol ingestion in a cat is, they immediately put the cat in his carrier and brought him in to Ruby Veterinary Urgent Care. No clinical signs associated with toxicity were noted at home prior to presentation, besides foaming which was suspected to be secondary to the taste of the capsule.

On examination, the cat was bright, alert, and responsive with normal vital parameters. No vomiting, facial swelling, dyspnea, or mucous membrane discoloration was observed at presentation. Given the high risk associated with acetaminophen ingestion in cats, we proceeded immediately with decontamination.

Vomiting was induced in a controlled hospital setting. Gastric contents were recovered; however, the missing capsule was not identified in the vomitus. Because the capsule was not recovered and ingestion could not be ruled out, we prepared to initiate treatment for suspected acetaminophen toxicity.

Acetaminophen (the active ingredient in Tylenol®) is extremely toxic to cats, even at low doses.

Cats have a limited ability to metabolize acetaminophen due to a deficiency in hepatic glucuronyl transferase enzymes. In other words, they lack one of the primary pathways used to safely process the drug. As a result:

• A larger proportion of acetaminophen is converted into a toxic metabolite (NAPQI).
• This metabolite causes oxidative damage to red blood cells and liver cells.
• Even small amounts can cause severe illness.

• As little as 10 mg/kg can cause clinical signs.
• Around 40–60 mg/kg can result in life-threatening toxicity. For many cats, this equates to part of a single regular-strength tablet.

Acetaminophen toxicity in cats primarily causes:

Methemoglobinemia

The toxic metabolite damages hemoglobin in red blood cells, converting it to methemoglobin, which cannot carry oxygen effectively. Clinical signs include:

• Brown or muddy-colored mucous membranes
• Rapid breathing
• Lethargy
• Weakness
• Hypothermia

2. Heinz Body Formation

Oxidative injury leads to fragile red blood cells and anemia.

3. Facial and Paw Edema

Swelling of the face and paws is common in cats.

4. Liver Injury

Although liver damage can occur, blood-related effects are often more dramatic and occur earlier in cats. Signs typically develop within 1–4 hours of ingestion.

Dogs metabolize acetaminophen more effectively than cats because they possess more robust glucuronidation pathways.

• Higher doses are required to cause toxicity.
• Liver damage (acute hepatic necrosis) is the primary concern.
• Methemoglobinemia can occur, but typically at higher doses.

• Liver toxicity: approximately 75–100 mg/kg
• Methemoglobinemia: often >200 mg/kg What may be a mild exposure in a dog can be fatal in a cat.

Because the capsule was not recovered, we prepared for full treatment protocol.

1. N-Acetylcysteine (NAC)

This is the antidote for acetaminophen toxicity. NAC:

• Replenishes glutathione stores
• Helps neutralize the toxic metabolite (NAPQI)
• Protects liver cells and red blood cells It is most effective when administered within 8 hours of ingestion but can still provide benefit later.

2. Activated Charcoal

May be administered to limit further absorption if ingestion was recent.

3. Oxygen Therapy

If methemoglobinemia develops.

4. IV Fluid Therapy

Supports circulation and liver function.

5. Vitamin C (Ascorbic Acid)

May help reduce methemoglobin levels.

6. Monitoring

• Packed cell volume (PCV) to monitor for anemia
• Methemoglobin levels
• Liver enzymes
• Clotting parameters Early, aggressive treatment dramatically improves survival.

Before antidotal therapy was initiated, the owners returned home to continue searching for the missing capsule. Fortunately, they located the intact capsule. The cat had not ingested the Tylenol®. Given this confirmation and the absence of clinical signs, no further treatment was required.

This case highlights several important points:

• Acetaminophen is one of the most dangerous over-the-counter medications for cats.
• Even suspected ingestion warrants immediate veterinary intervention.
• Cats are significantly more sensitive than dogs due to metabolic differences.
• Rapid treatment can be lifesaving. Thankfully, in this case, the missing capsule was found and the cat avoided what could have been a life-threatening emergency.