Be prepared to provide emergent supportive therapy. This may include airway protection or administration of vasopressors, intravenous (IV) fluid, or renal replacement therapy. N-acetyl cysteine (NAC) works as an antidote to prevent liver failure when used within a timely manner. It can be used for acute and chronic cases and works best if administered within 8 hours of acute ingestion. See N-acetyl cysteine administration for dosage / administration, indications, contraindications, monitoring, adverse effects, toxicity, and mechanism of action information. Fomepizole may be considered an adjunctive treatment in high-risk APAP overdose patients, particularly when time of ingestion is unknown. Consult a toxicologist.
About Acetaminophen and Acetaminophen Poisoning:
Acetaminophen, also known as paracetamol and N-acetyl-p-aminophenol (APAP), is one of the most widely used over-the-counter analgesics. APAP is also in many prescription pain relievers. When taken at supratherapeutic doses, it can cause significant liver toxicity due to increased production of its toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI) via the cytochrome P450 enzyme CYP2E1. NAPQI is a free radical molecule that causes hepatocellular damage.
Acetaminophen toxicity may occur with acute ingestion or chronic ingestions. In general, acute ingestions involve the consumption of acetaminophen as a single dose that results in a toxic concentration on the Rumack-Matthew nomogram. This typically correlates to an ingestion of 200 mg/kg of APAP in children and 150 mg/kg in adults.
Repeated ingestion of supratherapeutic doses of APAP (or even therapeutic doses taken too frequently) are more difficult to evaluate, as the Rumack-Matthew nomogram cannot be applied to these situations. History of recent acetaminophen use and elevated serum aminotransferases can be helpful in making this diagnosis. A detectable acetaminophen concentration can be helpful but is not necessary with a history of supratherapeutic acetaminophen use and elevated transaminase concentrations.
The natural history of acetaminophen toxicity occurs in 4 stages.
- Stage 1 occurs within 24 hours of ingestion. Patients may have nausea, vomiting, lethargy, and diaphoresis, or they may be asymptomatic.
- Stage 2 occurs between 24 and 72 hours after ingestion and is associated with elevated aminotransferases and right upper quadrant tenderness.
- Stage 3 occurs between 72 and 96 hours after ingestion and can present as hepatic encephalopathy, jaundice, coagulopathy, and acidosis.
- Stage 4 is the recovery phase and occurs between 96 hours and 2 weeks after ingestion; laboratory values may take longer to normalize.
Related topic: acute liver failure