Acetaminophen Toxicity Threshold for a 21-Year-Old Female (65 kg)
For this 21-year-old female weighing 65 kg, the acute toxicity threshold is 10 grams (10,000 mg) in a single ingestion or within 24 hours, which represents approximately 150 mg/kg—well above this patient's weight-based threshold of 9.75 grams. 1
Acute Single Ingestion Thresholds
The toxic dose requiring emergency evaluation is 10 grams OR 200 mg/kg (whichever is lower) for adults 6 years and older. 2 For this 65 kg patient, 200 mg/kg equals 13 grams, so the 10-gram threshold applies. 2
Any ingestion of 7 grams or more represents a potentially hepatotoxic dose and warrants treatment in most clinical scenarios, particularly for patients under 70 kg. 3 This patient at 65 kg falls into the higher-risk category where 7 grams exceeds 100 mg/kg. 3
Severe hepatotoxicity and mortality have been documented with ingestions ranging from 10-65 grams in adults. 1 The mean dose causing severe hepatotoxicity in intentional overdose patients was 23 grams per day. 1
Repeated Supratherapeutic Ingestion (RSTI) Thresholds
For repeated ingestions over multiple days, lower thresholds apply:
≥10 grams or 200 mg/kg (whichever is less) over a single 24-hour period requires emergency evaluation. 1, 2 For this patient, this equals 10 grams per day.
≥6 grams or 150 mg/kg (whichever is less) per 24-hour period for 48 hours or longer is potentially toxic. 1, 2 For this patient, this equals 6 grams per day for 2+ days.
Severe hepatotoxicity has been documented with doses as low as 4-5 grams per day when taken repeatedly, particularly in high-risk patients. 1
Maximum Therapeutic Dose
The FDA-recommended maximum daily dose for the general population is 4 grams (4,000 mg). 1 This represents the upper limit of safe therapeutic use.
Even therapeutic doses of 4 grams per day for 14 days can cause ALT elevations >3 times normal in 31-41% of healthy adults. 3, 1
Treatment Thresholds Using the Rumack-Matthew Nomogram
For single acute ingestions with known timing, acetaminophen levels above 200 mcg/mL at 4 hours post-ingestion or 50 mcg/mL at 12 hours post-ingestion indicate potential hepatotoxicity requiring N-acetylcysteine (NAC) treatment. 1
The nomogram is only valid for levels drawn 4-24 hours post-ingestion; levels drawn before 4 hours are unreliable and should be repeated. 3
Critical Timing for Treatment
NAC treatment initiated within 8 hours results in only 2.9% developing severe hepatotoxicity, compared to 6.1% when treated within 10 hours and 26.4% when treated 10-24 hours post-ingestion. 3, 1
Treatment should never be withheld even in late presentations (>24 hours), as NAC reduces mortality from 80% to 52% in fulminant hepatic failure regardless of timing. 3
Important Caveats
This patient has no underlying medical conditions, so standard thresholds apply. 3 However, certain risk factors would lower these thresholds:
Chronic alcohol consumption lowers the toxicity threshold to as low as 4 grams per day, with severe hepatotoxicity documented at 4-5 grams per day. 3, 1
Pre-existing liver disease significantly increases susceptibility to acetaminophen hepatotoxicity, requiring maximum daily doses limited to 2-3 grams. 1
Patients taking enzyme-inducing drugs (anticonvulsants) or with prolonged fasting/malnutrition have increased susceptibility. 2