Understanding and Managing Acetaminophen (Paracetamol) Overdose
Acetaminophen, also known as paracetamol, is a widely used over-the-counter medication for pain relief and fever reduction. While generally safe at therapeutic doses, it can cause significant toxicity when ingested in large amounts, leading to serious complications, especially hepatotoxicity. This article provides a comprehensive overview of acetaminophen overdose, its clinical presentations, diagnostic approaches, and management strategies based on current medical guidelines.
Understanding Acetaminophen Toxicity
Single Acute Ingestion
Adults:
- Lowest Acute Dose Capable of Causing Toxicity: 7.5 g
- Dose Causing Hepatotoxicity in Most Patients: 12 g (~150 mg/kg)
Children and Adolescents:
- Lowest Acute Dose Capable of Causing Toxicity: 150 mg/kg
- Dose Causing Hepatotoxicity in Most Patients: 200-350 mg/kg
- For Children <6 years old with unintentional ingestion, use a 200 mg/kg cutoff
[Toxic dose approximately 15 tabs]
Repeated Supratherapeutic Ingestions (Chronic Overdose)
Adults:
- >10 g or 200 mg/kg over a 24-hour period
- >6 g or 150 mg/kg per 24-hour period for at least 2 consecutive days (48 hours)
Children and Adolescents:
- <6 years of age:
- 200 mg/kg or more over a single 24-hour period
- 150 mg/kg or more per 24-hour period for the preceding 48 hours
- 100 mg/kg or more per 24-hour period for the preceding 72 hours or longer
- >6 years of age:
- At least 10 g or 200 mg/kg, whichever is less, over a single 24-hour period
- At least 6 g or 150 mg/kg, whichever is less, per 24-hour period for the preceding 48 hours or longer
Clinical Presentations of Acetaminophen Overdose
Acetaminophen overdose can be divided into four distinct stages, each with specific clinical manifestations and laboratory abnormalities.
| Stage | Timing | Clinical Manifestations | Laboratory Abnormalities |
| Stage 1 | First 24 hours | Anorexia, nausea, vomiting, malaise | Laboratory studies are typically normal |
| Stage 2 | Days 2-3 | Improvement in anorexia, nausea, and vomiting. Abdominal pain, hepatic tenderness | Elevated serum transaminases, elevated bilirubin, prolonged PT (if severe) |
| Stage 3 | Days 3-4 | Recurrence of anorexia, nausea, and vomiting. Encephalopathy, anuria, jaundice | Hepatic failure, metabolic acidosis, coagulopathy, renal failure, pancreatitis |
| Stage 4 | After day 5 | Clinical improvement and recovery (7-8 days) OR Deterioration to multi-organ failure and death | Improvement and resolution OR Continued deterioration |
Investigations
- Serum Acetaminophen Concentration: Helps determine the risk of toxicity.
- Liver Function Tests (AST, ALT): Elevations indicate hepatic injury.
- Electrolytes, BUN, Creatinine: Assess renal function and electrolyte imbalance.
- Coagulation Profile (PT, PTT, INR): Prolongation indicates severe liver damage.
- Blood Gas Analysis: To determine serum pH and assess metabolic acidosis.
Management of Acute Acetaminophen Poisoning
GI Decontamination
- Activated Charcoal: Most effective within the first 1-2 hours post-ingestion. Indicated if ingestion < 4 hr unless co-ingestants such as anticholinergic agents or opioids are present.
- Dose: 1 gm/kg (Max dose 50 gm) oral
- Contraindications: Gastrointestinal obstruction or altered mental status with an unprotected airway.
- Gastric Lavage: May be considered if ingestion < 1 hr. Not recommended for children.
Antidote: N-Acetylcysteine (NAC)
Indications for NAC Therapy in Children and Adolescents:
- Serum acetaminophen concentration above the "treatment" line.
- Single ingestion of greater than 150 mg/kg (7.5 g total dose regardless of weight).
- Unknown time of ingestion beyond 24 hours and a serum acetaminophen concentration >10 mg/L (66 micromol/L).
- Delayed presentation (>24 hours after ingestion) with laboratory evidence of hepatotoxicity and a history of excessive acetaminophen ingestion.
IV Regimens of NAC:
For Patients ≤ 20 kg:
- Diluent: 5%D/W or 0.45%NSS
- 3-Bag IV NAC regimen:
- NAC 150 mg/kg + 5%D/W 3 mL/kg IV over 60 min
- NAC 50 mg/kg + 5%D/W 7 mL/kg IV over 4 hrs
- NAC 100 mg/kg + 5%D/W 14 mL/kg IV over 16 hrs
For Patients >20 and <40 kg:
- Diluent: 5%D/W or 0.45%NSS
- 3-Bag IV NAC regimen:
- NAC 150 mg/kg + 5%D/W 100 mL IV over 60 min
- NAC 50 mg/kg + 5%D/W 250 mL IV over 4 hrs
- NAC 100 mg/kg + 5%D/W 500 mL IV over 16 hrs
- 2-Bag IV NAC regimen: Decreases adverse events with no change in efficacy.
- NAC 50 mg/kg/hour for 4 hours (200 mg/kg)
- NAC 6.25 mg/kg/hour for 16 hours (100 mg/kg)
For Patients > 40 kg:
- May receive IV NAC as recommended for adults.
- 3-Bag IV NAC regimen:
- NAC 150 mg/kg + 5%D/W 200 mL IV over 60 min
- NAC 50 mg/kg + 5%D/W 500 mL IV over 4 hrs
- NAC 100 mg/kg + 5%D/W 1,000 mL IV over 16 hrs
- 2-Bag IV NAC regimen: Decreases adverse events with no change in efficacy.
- NAC 200 mg/kg + 5%D/W 500 mL IV over 4 hrs
- NAC 100 mg/kg + 5%D/W 500 mL IV over 16 hrs
Follow-up and Monitoring
Before Completing NAC:
- Check: BUN, Cr, AST, ALT, PT, INR, and Acetaminophen level 1 hr before completing NAC therapy.
Decision to Discontinue NAC Therapy: NAC can be discontinued if all three of the following conditions are met:
- The patient is asymptomatic (e.g., no right upper quadrant pain).
- Acetaminophen concentration level is undetectable.
- Serum transaminase activity is decreasing significantly (has decreased to the normal range or to <50 percent of the peak value).
If Conditions Are Not Met: Continue IV NAC at a rate of 6.25 mg/kg per hour.
Conclusion
Acetaminophen overdose is a common and potentially life-threatening situation that requires prompt recognition and management. Understanding the stages of toxicity, conducting appropriate investigations, and implementing timely treatment, especially with N-Acetylcysteine, are critical for patient recovery. Clinicians should remain vigilant for signs of hepatic failure and ensure thorough monitoring and follow-up to guide the successful resolution of acetaminophen toxicity.