Assess acetaminophen overdose severity with Rumack-Matthew nomogram lookup, NAC dosing protocols (IV and oral), mg/kg calculation, and toxicity stage assessment for emergency management.
The Tylenol Overdose Calculator estimates acetaminophen ingestion severity, references the Rumack-Matthew nomogram to determine need for N-acetylcysteine (NAC) treatment, and calculates weight-based NAC dosing for both IV and oral protocols. Acetaminophen overdose is the most common cause of acute liver failure in the United States and United Kingdom, and rapid assessment is critical because NAC is nearly 100% effective at preventing hepatotoxicity when administered within 8 hours of ingestion.
The Rumack-Matthew nomogram is the cornerstone of acute single-ingestion management. It plots serum acetaminophen concentration against time since ingestion (4–24 hours) to determine if the patient falls above or below the 150 µg/mL treatment line. Patients above the line require NAC; those below can generally be observed. However, the nomogram has important limitations: it is not valid for chronic/repeated ingestions, extended-release products, unknown ingestion times, or measurements before 4 hours post-ingestion. In these situations, clinical judgment and empiric NAC are preferred.
This calculator provides the mg/kg ingestion dose (toxic threshold: ≥150 mg/kg), nomogram threshold at the entered time point, NAC dosing for the standard 21-hour IV protocol, the modified 2-bag IV protocol, and the 72-hour oral protocol. It includes severity staging, liver function assessment, and the clinical timeline of acetaminophen toxicity stages to support emergency department decision-making.
Acetaminophen overdose is the #1 cause of acute liver failure in developed countries. This calculator centralizes the critical decision tools — mg/kg ingestion severity, Rumack-Matthew nomogram reference, weight-based NAC dosing, and toxicity staging — into a single assessment for emergency department providers. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain.
Toxic dose threshold: ≥150 mg/kg (acute single ingestion) Rumack-Matthew nomogram: 150 µg/mL at 4 hours → 4.7 µg/mL at 24 hours (semi-logarithmic) NAC IV (21h): 150 mg/kg over 1h → 50 mg/kg over 4h → 100 mg/kg over 16h NAC Oral (72h): 140 mg/kg loading → 70 mg/kg q4h × 17 doses Activated Charcoal: 1 g/kg if ≤4 hours post-ingestion
Result: 200 mg/kg — High risk; Serum 180 µg/mL ABOVE nomogram line (150 µg/mL at 4h); NAC IV load: 10,500 mg
A 70 kg patient ingesting 14,000 mg (14 g) of acetaminophen = 200 mg/kg, well above the 150 mg/kg toxic threshold. At 4 hours post-ingestion, the serum level of 180 µg/mL exceeds the nomogram treatment line of 150 µg/mL. NAC should be started immediately using the 21-hour IV protocol: 10,500 mg (150 mg/kg) loading dose over 1 hour.
Published in 1975, the Rumack-Matthew nomogram revolutionized acetaminophen overdose management by providing an objective basis for treatment decisions. The original 200-line (probable toxicity) and 150-line (possible toxicity) were derived from analysis of untreated overdose outcomes. In practice, most US poison centers use the 150-line (also called the treatment line), while UK guidelines use the 100-line for additional safety margin. The nomogram assumes first-order elimination kinetics after peak absorption at 4 hours, which is why it plots as a straight line on a semi-logarithmic scale.
Several situations make the nomogram unreliable: co-ingestion of drugs that delay gastric emptying (opioids, anticholinergics) may delay APAP peak beyond 4 hours; extended-release formulations have biphasic absorption; massive ingestions (>500 mg/kg) may saturate metabolic pathways and show delayed clearance; and repeated supratherapeutic ingestions never achieve a single peak. In these cases, the nomogram should not be used as the sole decision tool. Clinical expertise, serial APAP levels, and liver function monitoring must guide management.
When acetaminophen hepatotoxicity progresses to fulminant liver failure, the King's College Criteria help identify patients who will likely die without transplantation. The criteria are: arterial pH < 7.3 after fluid resuscitation (regardless of grade of encephalopathy), OR all three of: Grade III/IV encephalopathy AND INR > 6.5 AND creatinine > 3.4 mg/dL. Patients meeting these criteria should be urgently referred to a transplant center.
The Rumack-Matthew nomogram is a graph plotting serum acetaminophen concentration vs. time post-ingestion (4–24 hours) on a semi-logarithmic scale. The treatment line starts at 150 µg/mL at 4 hours and declines to ~4.7 µg/mL at 24 hours. Patients above this line require NAC treatment. It is valid only for acute single ingestions with known timing.
NAC should be started within 8 hours of ingestion for maximum benefit (virtually 100% prevention of hepatotoxicity). After 8 hours, efficacy decreases but NAC still provides benefit up to 24 hours and beyond. If the ingestion dose is ≥150 mg/kg and the serum level won't be available within 8 hours, start NAC empirically.
Acute single ingestion ≥150 mg/kg (about 10,500 mg for a 70 kg adult) is considered potentially toxic and warrants serum level measurement and possible NAC treatment. Doses ≥250 mg/kg are high risk, and ≥500 mg/kg are considered massive with very high risk of severe hepatotoxicity.
IV NAC (21-hour or 2-bag protocol) is preferred due to faster completion, reliable delivery, and no GI absorption concerns. Oral NAC (72-hour protocol) is used when IV access is unavailable or in settings without IV preparation capabilities. Both are equally effective when started within 8 hours.
Acetaminophen absorption takes 1–4 hours for immediate-release formulations. Serum levels drawn before 4 hours may not reflect peak absorption and can underestimate toxicity. The Rumack-Matthew nomogram is validated starting at 4 hours, making this the earliest reliable time point for decision-making.
Extended-release formulations have delayed and prolonged absorption. A single 4-hour level may miss a late peak. Draw levels at 4 hours AND 8–10 hours post-ingestion. If either is above the nomogram line, treat with NAC. Initial levels below the line can be falsely reassuring.