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KembaraXtra-Medicine: Acetaminophen Poisoning
Acetaminophen (APAP) poisoning occurs when excessive amounts of acetaminophen are ingested, overwhelming normal hepatic metabolic pathways and leading to acute liver injury. If untreated, toxicity can progress to hepatic necrosis, liver failure, and death. Early symptoms are often nonspecific and include nausea, vomiting, diaphoresis, malaise, and abdominal discomfort, while later manifestations include jaundice, coagulopathy, hepatic encephalopathy, and multiorgan failure. Acetaminophen is also known as paracetamol, and poisoning is classified under ICD-10-CM codes T39.1 (accidental poisoning) and X60 (intentional self-poisoning).
Acetaminophen is among the most widely used antipyretic and analgesic medications worldwide and is present in over 100 prescription and over-the-counter combination products, including many cold, flu, and opioid formulations. In the United States alone, more than 100,000 potentially toxic ingestions are reported each year, making acetaminophen the most common pharmaceutical exposure reported to Poison Control Centers. It is the leading cause of acute liver failure and liver transplantation nationally. Nearly half of exposures occur in children younger than 6 years, often due to dosing errors. Individuals with chronic alcohol use disorder, malnutrition, chronic liver disease, or concurrent use of hepatotoxic drugs are at increased risk for severe toxicity.
The clinical course of acetaminophen poisoning typically follows four stages. During Stage I (0–24 hours), patients may be asymptomatic or experience nonspecific symptoms such as nausea, vomiting, anorexia, and lethargy, with laboratory studies often normal early on. Stage II (24–72 hours) marks the onset of hepatic injury, characterized by right upper quadrant abdominal pain, rising AST and ALT levels, and early abnormalities in coagulation or renal function. Stage III (72–96 hours) represents the period of maximal hepatotoxicity, with findings that may include hepatic encephalopathy, jaundice, coagulopathy, hypoglycemia, renal failure, metabolic acidosis, and death from multiorgan failure. Patients who survive this phase enter Stage IV (4 days to 2 weeks), during which hepatic regeneration occurs and clinical recovery is usually complete.
Acetaminophen toxicity results from the accumulation of N-acetyl-p-benzoquinone imine (NAPQI), a toxic metabolite normally detoxified by glutathione. When excessive acetaminophen is ingested, glutathione stores are depleted, allowing NAPQI to cause hepatocellular damage. The recommended maximum daily dose is 3-4 g in adults and 90 mg/kg in children. A single ingestion of ≥7.5 g in adults or ≥150 mg/kg in children is considered potentially toxic. Massive ingestions, often defined as >30–50 g, can produce early metabolic acidosis, altered mental status, and rapid progression to liver failure.
Diagnosis is based on history, timing of ingestion, and laboratory evaluation. A serum acetaminophen concentration obtained 4 hours or more after ingestion is plotted on the Rumack-Matthew nomogram to estimate the risk of hepatotoxicity and guide treatment decisions. The nomogram is not reliable in cases of unknown ingestion time, delayed presentation (>24 hours), chronic or staggered overdoses, or extended-release formulations. Additional laboratory studies include AST, ALT, INR, bilirubin, serum glucose, renal function tests, and screening for co-ingestants. Pregnancy testing is required in women of childbearing age.
Management centers on rapid initiation of therapy. Consultation with a Poison Control Center is strongly recommended. Activated charcoal may be administered within 4 hours of ingestion if the patient presents early. The definitive treatment is N-acetylcysteine (NAC), which replenishes glutathione, enhances non-toxic metabolism of acetaminophen, and improves outcomes even when started after liver injury has begun. NAC should be administered whenever toxicity is suspected or cannot be reliably excluded.
NAC may be given intravenously over 21 hours or orally over 72 hours. Intravenous NAC provides predictable absorption and a shorter treatment course but carries a risk of anaphylactoid reactions, whereas oral NAC is effective but commonly causes nausea and vomiting. Therapy should be continued if acetaminophen levels remain detectable, liver enzymes are elevated, or coagulopathy persists. In rare, severe cases with extremely high acetaminophen levels, metabolic acidosis, or altered mental status, hemodialysis may be indicated, with continued NAC administration.
All patients with confirmed acetaminophen poisoning require hospital admission, often to an intensive care unit for close monitoring. When treated promptly, prognosis is excellent, with approximately 90% of patients recovering fully. Acute liver failure is uncommon in young children. Psychiatric evaluation is necessary following intentional ingestions, and patient education on appropriate dosing and awareness of acetaminophen-containing combination products is essential to prevent recurrence.
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