Acetaminophen Toxicity

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

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 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

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

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