Tylenol Overdose
Level 180 mcg/mL at 4 hours - requires NAC
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Evidence-based calculations Used in clinical settings worldwide Regular monitoring recommended
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🚨 Above Treatment Line
Level 180 mcg/mL at 4 hours - requires NAC
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✅ Below Treatment Line
Level 50 mcg/mL at 8 hours - likely no NAC needed
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⚠️ Borderline
Level 150 mcg/mL at 4 hours - on the line
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💊 Large Ingestion
Estimated 20g ingestion in 70kg adult
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Example Cases
🚨 Above Treatment Line
Level 180 mcg/mL at 4 hours - requires NAC
✅ Below Treatment Line
Level 50 mcg/mL at 8 hours - likely no NAC needed
⚠️ Borderline
Level 150 mcg/mL at 4 hours - on the line
💊 Large Ingestion
Estimated 20g ingestion in 70kg adult
Patient Data
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
— WHO
— CDC
What is Acetaminophen Overdose?
Acetaminophen (paracetamol) overdose is the leading cause of acute liver failure in the United States. At therapeutic doses, acetaminophen is metabolized safely, but overdose depletes glutathione stores, allowing the toxic metabolite NAPQI to cause hepatocellular necrosis. N-acetylcysteine (NAC) is the antidote and is most effective when given within 8 hours of ingestion.
Toxicity Mechanism
NAPQI accumulates when glutathione is depleted, binding to hepatocytes and causing centrilobular necrosis.
Toxicity Timeline:
- Phase 1: 0-24h - GI symptoms
- Phase 2: 24-72h - Liver injury
- Phase 3: 72-96h - Peak injury/failure
NAC Antidote
N-acetylcysteine replenishes glutathione and is 100% effective if given within 8 hours.
NAC Routes:
- IV: 21-hour protocol (Acetadote)
- Oral: 72-hour protocol (Mucomyst)
- Still beneficial even late
Risk Factors
Some patients are at higher risk of hepatotoxicity at lower doses.
Higher Risk:
- Chronic alcohol use
- Fasting/malnutrition
- CYP2E1 inducers
How Does the Rumack-Matthew Nomogram Work?
The Rumack-Matthew nomogram is a semi-logarithmic plot that predicts hepatotoxicity risk based on serum acetaminophen level and time since ingestion. It is ONLY valid for acute, single ingestions with known time of ingestion. The "treatment line" starts at 150 mcg/mL at 4 hours and halves every 4 hours.
Above Treatment Line
NAC treatment required immediately. High risk of hepatotoxicity without treatment.
Treatment Line Values
4h: 150 | 8h: 75 | 12h: 37.5 | 16h: 18.8 | 20h: 9.4 | 24h: 4.7 mcg/mL
Below Treatment Line
Low risk of hepatotoxicity. NAC usually not indicated but may repeat level.
When Does the Nomogram NOT Apply?
Nomogram Limitations:
- • Unknown ingestion time - Cannot plot on nomogram
- • Multiple ingestions - Different kinetics
- • Extended-release products - Delayed peak
- • Level before 4 hours - Not yet at peak
- • Chronic/repeated ingestion - Different criteria
When to Treat Without Nomogram:
- • Estimated ingestion >150 mg/kg and level pending
- • Late presentation with elevated LFTs/INR
- • Chronic ingestion >150 mg/kg/day
- • Unknown time but high level
- • Extended-release with rising levels
NAC Treatment Protocols
21-Hour IV Protocol (Acetadote)
Bag 1: 150 mg/kg in 200 mL D5W over 1 hour
Bag 2: 50 mg/kg in 500 mL D5W over 4 hours
Bag 3: 100 mg/kg in 1000 mL D5W over 16 hours
Total: 300 mg/kg over 21 hours
72-Hour Oral Protocol (Mucomyst)
Loading: 140 mg/kg PO
Maintenance: 70 mg/kg PO every 4 hours × 17 doses
If vomiting: Give antiemetic, repeat within 1 hour
Total: 1330 mg/kg over 72 hours
Phases of Acetaminophen Toxicity
Acetaminophen toxicity progresses through four distinct phases. Early recognition is crucial because patients may appear well during the initial phase despite having potentially fatal ingestion.
0-24 Hours
Often asymptomatic or nonspecific symptoms
- • Nausea, vomiting, anorexia
- • Malaise, diaphoresis
- • Normal or mildly elevated LFTs
- • Patient may appear well!
24-72 Hours
Hepatotoxicity develops
- • Rising AST/ALT (may exceed 10,000)
- • Right upper quadrant pain
- • Prolonged PT/INR
- • Decreased GI symptoms
72-96 Hours
Maximum hepatotoxicity
- • Peak liver injury (AST/ALT)
- • Jaundice, coagulopathy
- • Hepatic encephalopathy possible
- • Acute kidney injury may occur
- • Death may occur in severe cases
4 Days - 2 Weeks
Recovery or liver failure
- • Survivors: complete recovery usual
- • LFTs normalize over 1-2 weeks
- • No chronic liver disease
- • Or progression to death/transplant
Special Populations
Certain populations have increased susceptibility to acetaminophen toxicity and may require treatment at lower thresholds.
Chronic Alcohol Use
- • CYP2E1 induction increases NAPQI
- • Depleted glutathione stores
- • Treat at lower threshold
- • Consider treatment line at 100 mcg/mL
Fasting/Malnutrition
- • Depleted glutathione
- • Eating disorders, chronic illness
- • HIV/AIDS, cancer cachexia
- • Lower threshold for treatment
CYP2E1 Inducers
- • Isoniazid (TB treatment)
- • Phenytoin, phenobarbital
- • Rifampin
- • Increase NAPQI production
When NOT to Use the Rumack-Matthew Nomogram
The nomogram was designed for single acute ingestions with known time. It should not be used in certain situations where empiric NAC treatment is appropriate.
Treat Empirically Without Nomogram
- Unknown time of ingestion
- Repeated supratherapeutic ingestions
- Extended-release formulations
- Level drawn <4 hours post-ingestion
- Presentation >24 hours post-ingestion
- Already elevated LFTs at presentation
- Ingestion >150 mg/kg with high-risk features
- Co-ingestion delaying absorption
NAC Adverse Reactions and Management
N-acetylcysteine is generally well-tolerated, but anaphylactoid reactions can occur, particularly with IV administration.
Anaphylactoid Reactions (10-20%)
- • Most common during first (loading) bag
- • Flushing, urticaria, pruritus
- • Nausea, vomiting
- • Bronchospasm (rare)
- • Hypotension (rare)
Management
- • Stop infusion temporarily
- • Diphenhydramine 25-50 mg IV
- • Albuterol for bronchospasm
- • Resume at slower rate once symptoms resolve
- • Do NOT discontinue NAC - benefits outweigh risks
Laboratory Monitoring
Serial labs help track hepatotoxicity progression and guide NAC treatment decisions.
Recommended Lab Schedule
Initial Labs
- Acetaminophen level at 4 hours (or ASAP if >4h)
- AST, ALT, PT/INR, bilirubin
- BMP (creatinine, electrolytes, glucose)
- Salicylate level (co-ingestion screen)
Serial Monitoring
- AST, ALT, PT/INR every 12-24 hours
- Repeat APAP level if extended-release
- Ammonia and lactate if encephalopathy
- ABG/VBG if severe (pH for King's criteria)
When to Stop NAC
NAC can be discontinued when the patient meets specific criteria indicating recovery from potential hepatotoxicity.
Standard Stopping Criteria
All of the following must be met:
- Acetaminophen level undetectable
- INR <2.0 (or improving)
- AST/ALT improving from peak
- Patient clinically improving
Continue NAC If:
- APAP still detectable
- INR >2.0 or still rising
- Transaminases still rising
- Any signs of hepatic failure
Clinical Pearls
Check Hidden Sources
Acetaminophen is in 600+ OTC products. Ask about Percocet, Vicodin, cold remedies, sleep aids.
NAC is Safe
When in doubt, give NAC. It has no contraindications and can be stopped if level returns below treatment line.
Don't Trust History
Patients may underestimate dose or be unreliable historians. Get a level at 4 hours regardless of stated dose.
Activated Charcoal
Consider if within 4 hours and no contraindications. Does not interfere with NAC efficacy.
King's College Criteria
For liver transplant evaluation: pH <7.3, or INR >6.5 + creatinine >3.4 + grade 3-4 encephalopathy.
Consult Toxicology
For complex cases, extended release ingestions, or when to stop NAC. Call Poison Control: 1-800-222-1222.
Frequently Asked Questions
What is the maximum safe daily dose of acetaminophen?
For healthy adults, maximum is 4g/day (4000mg). For those with chronic alcohol use, liver disease, or fasting states, maximum is 2g/day. Single toxic dose threshold is generally >150 mg/kg.
Why must the level be drawn at 4 hours?
Absorption may not be complete before 4 hours. A level drawn earlier could be falsely low. The Rumack-Matthew nomogram is only validated for levels at ≥4 hours post-ingestion.
Is NAC still effective after 24 hours?
Yes, but efficacy decreases. NAC is most effective within 8 hours but still provides benefit even after hepatotoxicity develops by improving survival through multiple mechanisms.
Can pregnant patients receive NAC?
Yes. NAC is safe in pregnancy and should not be withheld. APAP overdose poses greater risk to mother and fetus than NAC treatment. Standard protocols apply.
What about extended-release acetaminophen overdose?
Extended-release formulations may have delayed or prolonged absorption. Get serial APAP levels and don't rely solely on a single 4-hour level. Consider empiric NAC if ingestion history suggests toxic dose.
Should I give activated charcoal?
Consider activated charcoal 1g/kg (max 50g) if within 4 hours of ingestion and the patient is alert with protected airway. It does not interfere with oral NAC. Not indicated after significant time has passed.
Prevention and Patient Education
Safe Use Guidelines
- • Never exceed 3000-4000 mg/day
- • Wait at least 4-6 hours between doses
- • Read all medication labels for hidden acetaminophen
- • Avoid alcohol when using acetaminophen regularly
- • Keep medications locked away from children
When to Seek Help
- • Any suspected overdose - immediate ER visit
- • Nausea, vomiting, abdominal pain after acetaminophen
- • Accidental double-dosing in children
- • Call Poison Control: 1-800-222-1222
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