Acetaminophen Toxicity in Pets

Acetaminophen Toxicity – An Overview

Results from owners overdosing the pet with over-the-counter medications containing acetaminophen, a medication intended to control pain or fever in humans

Signalment/Description of Pet

Young and small dogs – greater risk from owner-given single-dose acetaminophen medications

Signs/Observed Changes in Pet

May develop 1–4 hours after dosing
Progressive depression
Rapid breathing
Darkened mucous membranes (moist tissues of body, such as gums)
Drooling (salivation)
Vomiting
Abdominal pain
Rapid breathing (known as “tachypnea”) and bluish discoloration of skin and moist tissues of body (known as “cyanosis”) due to a abnormal compound (methemoglobin) in the blood (condition known as “methemoglobinemia”) that disrupts the ability of the red blood cells to carry oxygen to the body
Fluid buildup (edema)—face, paws, and possibly forelimbs; after several hours
Chocolate-colored urine due to the presence of blood in the urine (known as “hematuria”) and the presence of methemoglobin in the urine (known as “methemoglobinuria”);
Death

Causes

Acetaminophen overdosing

Risk Factors

Nutritional deficiencies of glucose and/or sulfate
Simultaneous administration of other glutathione-depressing drugs

Treatment for Acetaminophen Toxicity in Animals

Health Care

With methemoglobinemia (abnormal compound [methemoglobin] in the blood that disrupts the ability of the red blood cells to carry oxygen to the body)—must evaluate promptly; inpatient care
With dark or bloody urine or yellowish discoloration of skin and moist tissues of the body (known as “jaundice” or “icterus”)—inpatient care
Gentle handling—imperative for clinically affected pets
The pet veterinarian will induce vomiting (known as “emesis”) and may perform flushing of the stomach (known as “gastric lavage”)—useful within 4–6 hours of ingestion of acetaminophen
Low red blood cell count (known as “anemia”), blood in the urine (hematuria), or presence of hemoglobin in the urine (known as “hemoglobinuria”)—may require whole blood transfusion
Fluid therapy to maintain hydration and electrolyte balance
Drinking water should be available at all times

Activity

Restricted

Diet

Food—offered 24 hours after initiation of treatment

Medications for Acetaminophen Toxicity in Pets

Medications presented in this section are intended to provide general information about possible treatment. The treatment for a particular condition may evolve as medical advances are made; therefore, the medications should not be considered as all inclusive

Activated charcoal—administered immediately after the veterinarian has induced vomiting or flushed the stomach (gastric lavage) and after vomiting is controlled; activated charcoal is used to attract and keep the remaining acetaminophen in the gastrointestinal tract
N-acetylcysteine (Mucomyst®) is administered; considered to be an antidote for acetaminophen toxicity
Other sulfur donor drugs—if N-acetylcysteine not available; sodium sulfate
1% methylene blue solution—combats methemoglobinemia without inducing red blood cell destruction (known as a “hemolytic crisis”)
Ascorbic acid—slowly reduces methemoglobinemia

Follow-Up Care

Patient Monitoring

Continual clinical monitoring of methemoglobinemia (abnormal compound [methemoglobin] in the blood that disrupts the ability of the red blood cells to carry oxygen to the body)
Serum liver enzyme activities to monitor liver damage
Blood glutathione level—provide evidence of the effectiveness of therapy

Preventions and Avoidance

Give careful attention to acetaminophen dose; acetaminophen should only be given to dogs under a veterinarian’s supervision

Possible Complications

Liver damage and resulting scarring (fibrosis)—may compromise long-term liver function in recovered pets

Expected Course and Prognosis

Rapidly progressive methemoglobinemia (abnormal compound [methemoglobin] in the blood that disrupts the ability of the red blood cells to carry oxygen to the body)—serious sign
Methemoglobin concentrations greater than 50%—grave prognosis
Progressively rising serum liver enzymes 12–24 hours after ingestion—serious concern
Expect clinical signs to persist 12–48 hours; death owing to methemoglobinemia possible at any time
Receiving prompt treatment that reverses methemoglobinemia and prevents excessive liver damage may recover fully
Death as a result of liver damage may occur in a few days

Key Points

Acetaminophen should only be given to dogs under a veterinarian’s supervision
Considerably less frequent in dogs
Treatment in clinically affected pets may be prolonged and expensive
Pets with liver injury may require prolonged and costly management