Paracetamol (acetaminophen) overdose: treatment line check

Toxicology

Single acute overdose with a known time of ingestion, level taken 4 to 24 hours after it. Compares the level with the treatment line. It does not apply to staggered or repeated ingestion, or when the time is uncertain.

What you enter

Hours since ingestion (use the earliest possible start time) (h)
Plasma paracetamol level (mg/L or µg/mL or µmol/L)
Treatment line in use: 150 mg/L at 4 h (US, Canada, Australia) / 100 mg/L at 4 h (UK since Sep 2012)
Modified-release product, or 500 mg/kg or more taken (0)
Staggered or repeated ingestion, or time of ingestion uncertain (0)

FORMULALine = start x 2^(-(hours - 4) / 4), a 4-hour half-life, from 4 to 24 h. The 150 line reaches 18.75 mg/L at 16 h; the 100 line runs parallel to it. 1 mg/L = 6.62 µmol/L.

SourceRumack BH, Matthew H. Acetaminophen poisoning and toxicity. Pediatrics 1975;55(6):871-6 (original line 200 mg/L at 4 h; the 150 treatment line was set 25% below it). UK single 100 mg/L line: MHRA acetylcysteine licence change, 3 Sep 2012. Caveats: Ontario Poison Centre nomogram sheet (Feb 2022); NHS GGC paracetamol overdose guidelineReviewedFormula and thresholds checked against the source on 2026-09-29. If the source updates, this line will say so.